Periods can last anywhere from three to seven days, but your “normal” period is whatever is typical for you. If it suddenly changes, it may be due to a change in schedule, birth control, pregnancy, or stress.

Here’s what to watch for and when to see your doctor.

It’s normal for your menstrual cycle to change at different times in your life.


During puberty, your hormone levels begin to fluctuate on a monthly cycle. It takes a few years for these hormones to develop a regular schedule. In the meantime, they can be irregular, leading to shorter or longer periods.

Other menstrual symptoms common during puberty include:

  • irregular periods
  • light or heavy bleeding
  • missed periods
  • two periods per month


Perimenopause is the time leading up to your final period. During this time, your hormone production decreases and periods typically become irregular.

Your periods may be shorter or longer than usual. You may also experience:

  • missed periods
  • light or heavy bleeding
  • irregular periods
  • fewer periods per year

Changes in your daily routine can impact your hormone levels and cause irregular periods.


Stress takes a toll on your whole body, including your ability to produce hormones. When your hormone levels are affected by stress, it isn’t uncommon for your period to become irregular. This may include less days spent bleeding.

Other symptoms of stress include:

Excessive exercise or athletic activity

When you exercise excessively, it’s easy to burn more calories than you eat. If this goes on for weeks or months, your body will enter starvation mode.

Your body will begin to use all of its remaining fuel (calories) to perform critical functions, like keeping your heart beating, at the expensive of other functions, like producing reproductive hormones.

When your hormone levels decrease, it can cause irregular or missed periods.

Excessive physical activity can also cause:

  • mood swings
  • tiring more easily
  • getting sick more often
  • unintentional weight loss

Significant weight changes

Any significant changes in weight can disrupt your normal hormone levels. Following gastric bypass surgery and extreme dieting, many women experience irregular periods.

Excess body fat can also affect estrogen levels, which means obesity can impact your menstrual cycle.

Other side effects of major weight changes include:

  • headaches
  • fatigue
  • missed periods

Eating disorder

Eating disorders that involve extreme calorie restriction can affect the body’s ability to produce reproductive hormones. A very low body fat percentage can also disrupt normal hormone levels. This can cause irregular, short, or missed periods.

Other symptoms of eating disorders include:

Many common medications can affect your hormone levels and change your menstrual cycle.

Hormonal birth control

Hormonal birth control methods contain hormones that directly affect when and how you ovulate. When you start birth control for the first time or switch to a different kind, it’s normal to experience some changes to your menstrual cycle.

You may experience shorter periods or irregular periods for a few months, until your body gets used to the new medication.

Other side effects commonly seen with the pill, the birth control shot, and the hormonal IUD include:

  • cramping
  • spotting
  • headaches

Other medications

Certain prescription medications can interfere with your body’s hormones and cause irregular periods.

Medications that cause irregular periods include those for:

There are several underlying conditions that can affect your hormone levels and cause you to have shorter periods than normal.

Ectopic pregnancy

An ectopic pregnancy happens when a fertilized egg implants itself in an area of the body other than the uterus. Ectopic pregnancies often cause vaginal bleeding that may be mistaken for a period.

Other signs of an ectopic pregnancy include:

  • abdominal pain
  • dizziness
  • shoulder pain


Implantation is when a fertilized egg embeds itself in the wall of your uterus. It occurs about one to two weeks after inception. In some cases, it can cause minor vaginal bleeding that may be mistaken for a short period.

Implantation often occurs before you miss a period and develop other symptoms of pregnancy.


A miscarriage is an event that results in the loss of embryonic tissue or a fetus during pregnancy. Miscarriages often take place before women know that they’re pregnant, which is why they’re often mistaken for periods.

A short, unexpected period could be a miscarriage.

Other symptoms of miscarriage include:

  • spotting or bleeding
  • passing fluid or tissue from the vagina
  • abdominal pain


Periods stop during pregnancy, but it isn’t unusual for there to be spotting or light bleeding in the first trimester of pregnancy. Up to one in four women experience some bleeding during pregnancy.

Other symptoms of pregnancy include:

  • sore or swollen breasts
  • nausea
  • vomiting
  • missed period
  • cravings or aversion to foods or smells


The hormone that helps you to produce breastmilk, prolactin, also stops you from ovulating. If you’re breastfeeding day and night, your period may not return for several months after giving birth.

When your period does return, it may be irregular and shorter or longer than usual.

When breastfeeding, you may also experience:

  • missed periods
  • months between periods
  • changes in period duration
  • light bleeding or spotting at first

Ovarian cyst

An ovarian cyst is a fluid-filled sac inside the ovary. While these cysts aren’t cancerous, they can sometimes be painful or cause bleeding. A bleeding cyst may be mistaken for a short period.

Most ovarian cysts have no symptoms, but they can sometimes cause abdominal pain, particularly if they’re large or if they rupture.

Polycystic ovarian syndrome (PCOS)

PCOS can cause your body to produce more male sex hormones than normal. This hormonal imbalance often causes irregular periods, missed periods, or short periods.

Other symptoms of PCOS include:

Thyroid disorder

Thyroid disorders cause the body to produce too much or too little thyroid hormone. Thyroid disease affects about one in eight women.

Thyroid hormone plays an important role in your menstrual cycle and can cause a variety of menstrual irregularities, including short periods.

Symptoms of thyroid disorder vary depending on which type you have, but may include:

  • weight loss or gain
  • trouble sleeping or sleepiness
  • fast heart rate or slow heart rate
  • lighter or heavier than normal periods

Rarely, short periods are caused by a more serious condition.

Premature ovarian failure (POF)

POF is when you go into early menopause. POF is rare, affecting only 1 in 1,000 women under the age of 29 and 1 in 100 women between ages 30 and 39.

If your ovaries fail, it means you no longer produce the necessary hormones to become pregnant. Your periods may become irregular and then stop entirely. POF may also cause:

  • hot flashes
  • missed periods
  • irregular periods
  • vaginal dryness

Asherman syndrome

Asherman syndrome is a rare condition in which scar tissue develops in the uterus. This typically presents after a surgical procedure.

Uterine scar tissue may block the flow of your period, causing irregular or missed periods.

Other symptoms include:

  • missed periods
  • difficult conceiving
  • miscarriages
  • cramping without bleeding

Cervical stenosis

Cervical stenosis is the abnormal narrowing of the cervix, which is very rare. It typically happens as a complication of surgery. When the cervix narrows, your mensural flow is obstructed. It may cause missed periods and abdominal pain.

Sheehan’s syndrome

Sheehan’s syndrome is a complication of childbirth that occurs when a woman loses large amounts of blood or experiences severe low blood pressure. It’s very rare in advanced countries where people have access to medical treatment.

Sheehan’s syndrome interferes with the body’s ability to produce pituitary hormones. Low hormone levels lead to absent or infrequent periods.

Other symptoms include:

  • difficulty breastfeeding
  • difficulty regrowing shaved pubic hair
  • low blood pressure
  • weight gain
  • fatigue

If you’re pregnant or suspect you could be pregnant, you should seek emergency medical treatment if you have any unusual bleeding.

Otherwise, you can typically wait two to three months before seeing your doctor. This will allow your menstrual cycle time to reset and return to normal.

Consider tracking your periods during this time. Make sure you note your period’s start and stop dates, along with details about when bleeding is heavy or light. Your doctor can use this information to help make a diagnosis.