An early period here and there usually isn’t cause for concern.

Everyone’s menstrual cycle is different. Your cycle starts on the first day of your current period and ends on the first day of your next period.

A typical cycle lasts anywhere from 21 to 39 days, so the number of days spent bleeding varies from person to person. Most people bleed for two to seven days.

If your cycle is frequently shorter than 21 days — leading you to bleed earlier than you normally do — it could be a sign of something underlying.

Read on to learn which symptoms to watch for and when to see your doctor.

Puberty typically starts between ages eight and 13. It’s driven by chemicals in your body called reproductive hormones. These hormones will continue to affect your menstrual cycle throughout your child-bearing years.

In the first few years after you get your period, these hormones can be irregular. This means that the number of days between your periods may be shorter or longer than average.

Puberty can also cause:

  • enlarged breast tissue
  • hair to develop on the armpits and groin
  • pimples
  • moodiness

Perimenopause is the transition into menopause. It typically begins in your mid to late forties and lasts about four years.

Your hormone levels fluctuate wildly during this time, and you may not ovulate every month. This can cause irregular periods, so you may menstruate sooner or later than usual.

Perimenopause can also cause:

  • periods to be lighter or heavier than normal
  • missed periods
  • vaginal dryness
  • hot flashes
  • difficulty sleeping
  • irritability

Intense exercise can cause irregular periods or cause your period to stop altogether. Often, this condition is associated with athletes who train for several hours daily. It’s most common in sports with weight constraints, like ballet and gymnastics.

Exercise only affects your periods when you burn way more calories than you eat. Without adequate energy, your body doesn’t produce the amount of reproductive hormones it needs to ovulate normally.

Early, irregular, or missed periods are often associated with major weight changes. Period irregularities often occur with rapid weight loss. This can happen with extreme dieting, gastric bypass surgery, or eating disorders.

When the body enters starvation mode, it reserves its energy for essential life functions, like breathing. Your body will stop producing reproductive hormones, which leads to period irregularities.

Severe stress can disrupt your hormone levels, causing irregular periods. If you experience anxiety or have recently been through a traumatic event, this may throw your hormones out of whack.

Stress can also cause:

  • unexplained weight gain or loss
  • difficulty sleeping
  • difficulty concentrating

Changes in your normal routine can affect your hormones and cause your period to come early or late. For example, some research suggests that people who switch between day and night shifts, like nurses, often experience irregular periods. Switching time zones may have similar effects.

Researchers don’t know exactly why this happens, but it may be related to a disruption in your circadian rhythm. This may, in turn, disrupt the sleep hormone melatonin.

More research is needed to explore a connection between melatonin and reproductive hormones.

Taking blood thinners (anticoagulants) may prolong your period and cause heavy bleeding.

Anticoagulants are released naturally during your period to help thin the lining of your uterus, so it can flow out of the vagina. Taking anticoagulants may cause this process to happen faster and result in a heavier flow.

The hormones present in hormonal birth control directly affect ovulation and menstruation.

If you’re taking birth control pills, the timing of your next period will depend on when during your cycle you started taking the pills and whether you’re taking a week of placebos (reminder pills).

Other hormonal birth control options, like intrauterine devices (IUDs) and the Depo-Provera shot, can cause menstrual irregularities for the first two or three months. Side effects include irregular periods or daily breakthrough bleeding.

As you adjust to hormonal birth control, you may also experience:

  • cramping
  • sore breasts
  • headaches
  • nausea

Emergency contraception (EC) is used to reduce your risk for pregnancy after having unprotected sex. You can get an EC pill or have a copper IUD inserted as EC.

EC pills contain hormones that disrupt the normal ovulation process. This may lead to an early or late period. If you use EC pills routinely, your period may become irregular.

It isn’t uncommon for people to experience breakthrough bleeding after their doctor inserts an IUD. It takes your uterus a few months to get used to the IUD, during which time you may bleed daily or irregularly.

Copper IUDs can also cause:

  • heavy periods
  • severe menstrual cramps
  • cramping or backaches

STIs like chlamydia and gonorrhea are quite common. These bacterial infections typically don’t cause symptoms. When they do, they’re known to cause spotting between periods or blood-tinged discharge.

They may also cause:

  • pain during sex
  • pain or burning when peeing
  • abdominal pain

PCOS is a common condition caused by a hormonal imbalance. It affects 1 in 10 females of child-bearing age.

Many people don’t know they have PCOS until they have difficulty becoming pregnant. It can also cause:

Endometriosis occurs when the tissue that lines your uterus begins to grow outside of the uterus. It affects around 11 percent of females in the United States between the ages of 15 and 44.

In addition to unexpected bleeding, endometriosis can cause:

  • severe menstrual cramps
  • chronic lower back pain
  • pain during or after sex

When diabetes is undiagnosed or poorly managed, blood sugar levels are chronically higher than normal. One 2011 study found that many people with type 2 diabetes had irregular periods in the years leading up to their diagnoses.

Diabetes can also cause:

  • increased thirst
  • increased need to urinate, especially at night
  • slow healing
  • sudden weight loss

It’s thought that one in eight females will develop a thyroid condition in their lifetime.

Thyroid conditions cause your body to make more or less thyroid hormone than your body needs. This hormone is essential to several body functions, including your metabolism and menstrual cycle.

Your individual symptoms will depend on whether your thyroid is underactive or overactive. In addition to early menstruation, you may experience:

  • periods that are light or heavier than usual
  • a heart rate that’s faster or slower than usual
  • difficulty sleeping
  • unexpected weight loss or gain

Implantation occurs when a fertilized egg attaches to the lining of your uterus. It happens one to two weeks after conception.

Implantation doesn’t always cause symptoms. When symptoms do occur, they include light bleeding or cramping. Bleeding is typically lighter than a normal period and usually won’t require a tampon or pad.

If you’ve had unprotected sex or experienced birth control failure since your last period, you may consider buying a couple of over-the-counter pregnancy tests. You can take one now, but it may still be too early to register an accurate result.

If you can, wait to take the test until a week after your regular period was supposed to start. You can also see your doctor to confirm your results.

A miscarriage is the loss of a pregnancy. Most miscarriages take place during the first trimester. It often happens before the person is aware of the pregnancy, so it can be difficult to differentiate between a particularly heavy period and a miscarriage.

A miscarriage may cause more cramping and back pain than a normal period.

If the pregnancy was farther along, pink discharge, blood clots, or pieces of fetal tissue pass from the vagina.

If you believe you have miscarried, seek immediate medical attention.

If you’ve expelled any unusual tissue and are able to collect it, bring it with you. Your doctor will assess the tissue and use it to make a diagnosis.

Your doctor will also perform a pelvic exam and ultrasound to determine whether a miscarriage took place. In some cases, they may need to remove lingering tissue from your uterus.

How you manage your period will depend on what you think is causing it to come early. In most cases, an early period will resolve itself in a month or two.

You may be able to get your cycle back on track if you:

  • Use a period app. Period tracking apps allow you to log your day-to-day symptoms. Over time, you may notice a pattern in your flow. You can also share your logs with your doctor at your next appointment.
  • Stay prepared. Keep a few panty liners, pads, or tampons in your bag or at work so you aren’t caught off guard. For added protection, consider investing in a set of period underwear.
  • Get eight hours of sleep every night. An abnormal sleep schedule can throw your period off track. If you work nights, do the best you can to maintain your circadian rhythm by sleeping in a dark and quiet environment during the day.
  • Eat a healthy, balanced diet. Proper nutrition is key to a healthy reproductive system. If you aren’t consuming enough calories, your body can’t produce the hormones it needs to maintain regular functioning.
  • Don’t train too hard. When you burn more calories than you take in, your body doesn’t have the energy to adequately produce reproductive hormones. Consider supplementing your diet with high-calorie protein shakes.
  • Manage your stress. Psychological stress can throw a wrench in your menstrual cycle. If your home or work life is getting on top of you, carve out some time to watch an episode of something you enjoy, go on a walk, or practice yoga.
  • Maintain a healthy weight. Obesity can interfere with your reproductive hormones. Starting an exercise plan with a friend or joining a diet support group, like Weight Watchers, can help you reach a healthy weight.

An early period usually isn’t a sign of anything serious. But if you’re in severe pain or discomfort, you should see your doctor.

You should also seek immediate medical attention if you’ve experienced a miscarriage, or suspect that you have.

If you aren’t experiencing any severe symptoms, you may be able to regulate things at home. Consider tracking your periods for the next two to three months to see how your timing, flow, and other symptoms compare.

If things aren’t leveling out, talk to your doctor. They can use this information to evaluate your cycle and advise you on any next steps.