You’re exhausted, your breasts are swollen, your period is 5 days past due… and is that a twinge of morning sickness you’re feeling? Could you be pregnant?

We would say there’s only one way to tell — take a pregnancy test! — but that’s actually kind of untrue: Over-the-counter pregnancy tests are a quick and convenient way to know if you’re pregnant, but they’re nowhere near 100 percent reliable.

There are false negatives, false positives, and every result in between. (Hands up if you’ve ever been caught holding that pee-soaked stick under a light while you try to decode symbols that look like Egyptian hieroglyphics… yeah, us too).

Why is it so hard to find out at home if you’re pregnant, especially when you’ve got the sore boobs and queasy stomach to back it up? It turns out there are a lot of reasons why you might feel pregnant but end up with a minus sign — here are 10 of them.

Related: The best pregnancy tests of the year

You know how pregnancy tests say you can “test 5 days sooner!” on the package? That refers to how many days before your expected period you can test yourself and get an accurate result.

But if you read the fine print, the likelihood of accurate results starts out kinda small at the 5-day mark, increasing as you get closer to your period.

If it’s way too far from your expected period date, you won’t have enough pregnancy hormone in your urine yet to trigger a positive result on the test.

The easiest solution here is to simply wait a few days, or even all the way until you’re past due for your period (hard to do, we know!). Even re-testing again in 72 hours, though, could land you a different result.

OK, so you waited until you actually missed your period and the test still came up negative?

Time to consider the time of day you peed on the stick. If you’re very newly pregnant, your hCG levels (that’s human chorionic gonadotropin, for the uninitiated, a hormone produced by a growing placenta) could still be on the lower side, especially later in the day when your urine is more diluted by what you’ve had to drink.

For more accurate results, test yourself first thing in the morning so you’re using your most potent urine. Icky, but effective!

The more diluted your urine is, the less hCG will be present — and the less likely you are to get a positive result. What dilutes your urine? Good ol’ H20.

If you’re a committed hydrator (we see you with your half-gallon HydroJug), it’s possible you’re too good at flushing out your system. Who knew?

Don’t cut back entirely on water, just don’t drink too much the night before or the morning of taking your test.

Even though they’re pretty straightforward, reputable pregnancy tests always include instructions.

And while most pregnancy tests are designed to work the same basic way (and it’s not rocket science anymore, thankfully), you still need to perform your specific brand of test accordingly.

If you didn’t pee on the right part of the testing strip, didn’t lay the test down flat and faceup, or if you let it sit for too long on your bathroom vanity before checking, it can mess up your results.

Just like any other mass-manufactured product, pregnancy tests can arrive at the store damaged, expire on the shelves or in the back of your bathroom cabinet, get exposed to too-high or too-low temperatures during transit, or just… not work. Nothing’s perfect!

We don’t want to give you the kind of false hope that sends you running out for duplicate and triplicate tests every time you get a negative result, but it is possible for tests to malfunction.

If you have a legit reason to think something may have been wrong (looking at you, tests from the Dollar Store checkout line), by all means buy a fresh test from a different store and try again.

But maybe take a break after that — it’s unlikely you’ll get two faulty tests in a row.

Because we like to keep you in-the-know, there are some less-common scenarios that can lead to a false negative on a pregnancy test:

  • Ectopic pregnancy. When a fertilized egg implants somewhere outside the uterus, it’s called an ectopic pregnancy and, sadly, it’s not viable. Because your placenta won’t grow like it should, your hCG levels won’t always rise to detectable amounts (although in many cases they will, and you’ll get a positive test) — but you may have pregnancy symptoms. These types of pregnancies are rare but can turn serious if left untreated, so if you also have severe pain or vaginal bleeding, seek medical care ASAP.
  • Cryptic pregnancy. It’s super rare, and often the stuff sensational news stories are made of, but it’s possible to have a cryptic pregnancy that conventional pregnancy tests never detect. There are varying reasons for this, including certain conditions that cause fluctuating hormone levels that may give you period-like bleeding — thus preventing you from taking a test until a later stage of pregnancy. (See next bullet point.)
  • Later-state pregnancy. Most OTC pregnancy tests are designed to recognize hCG levels within a certain range, so if your hCG levels are lower or higher than what the test is able to detect, you’ll get a negative result. When hCG levels are so high that the test misses them completely, it’s called the “hook effect,” and it can happen when you’re further along in your pregnancy than just a few weeks. Hormones rise continually throughout pregnancy; if you have irregular periods or lost track of when you were last supposed to get one, you could be far enough along in your pregnancy that an OTC test won’t read your higher levels of hCG.

In these cases, a blood test or ultrasound performed at your doctor’s office is the best way to confirm if you are, in fact, pregnant.

You know what medical condition feels a lot like pregnancy? Menstruation.

The same body system and hormones are involved, so it makes sense. Rising levels of progesterone during PMS can cause symptoms that mimic pregnancy to a T, whether it’s tender breasts, a ravenous appetite, mild cramping, moodiness and fatigue, spotting, or even nausea.

When you’re newly pregnant, your progesterone levels also rise, so these two events can, unfortunately, cause some confusing overlap in how they make you feel.

The solution here is just to wait a few days: If you’re PMSing, you’ll get your period, and if you’re pregnant, you won’t (and another pregnancy test in a few days may let you know).

Ovulation — which happens about midway through a typical cycle — doesn’t have as many symptoms in common with pregnancy as menstruation does, but you could still experience breast tenderness, mild cramping, and occasionally nausea during the time when your uterus releases its monthly egg.

If you’re not tracking your periods and don’t know exactly where you are in your cycle, you could be forgiven for mistaking ovulation for early signs of pregnancy… but you may have to wait around 12–15 days before finding out if your fertile window was fruitful.

Here’s the tricky thing many of us have found about wanting to be pregnant really badly: Sometimes, that desire is so intense that your brain has a hard time thinking of anything else.

We get it — once you decide you’re ready for a baby, getting a negative test result can be crushing.

Your very real desire can lead to symptom spotting, and to be honest, Dr. Google doesn’t help.

Put in any symptom + pregnant and you’re bound to get some hits. Your nausea isn’t because you skipped breakfast, it’s because you’re pregnant. Your fatigue isn’t because you started a new diet, it’s because you’re pregnant.

When you put on pregnancy-tinted glasses, it’s hard to think objectively.

If you can, try to avoid the symptom spotting trap. If you are pregnant, you’ll know soon… but if it turns out you’re not, you may end up feeling even more disappointed.

If you’ve been having trouble conceiving and are undergoing fertility treatments, remember that those drugs are designed, in part, to elevate your hormone levels.

Therapies that increase progesterone or block estrogen can cause symptoms that mimic both PMS and pregnancy, including nausea, bloating, tender breasts, and changes in mood.

If you’re not sure whether your pregnancy-like symptoms are due to actual pregnancy or just a side effect of whatever fertility treatments you’re on, give your OB-GYN or reproductive medicine doctor a call. They should know where you are in your cycle and whether it’s possible you could be pregnant (or not).

Almost everything having to do with pregnancy involves waiting: waiting until your period is due to take a pregnancy test, waiting those looooooong 3 minutes to check the results, waiting until the next month to try again, waiting 9 whole months for your baby to be born once you actually get pregnant.

In other words, nothing is instantaneous and there are a lot of unknowns.

This can make the journey to having a baby more than a little rocky. To cope, try these tips:

  • Stay in the present. You can’t change the past or predict the future, right? Take it one day at a time.
  • Maintain a mutual hobby or activity with your spouse or partner that doesn’t involve baby making. You’re still a couple, and it’s important to protect the health of your relationship.
  • Find your inner peace. When you feel yourself getting stressed about conceiving, have a go-to activity that calms you down. Make it something you look forward to, so it’s more of a positive experience and less of a consolation prize.
  • Have a backup plan. If you’re hoping to conceive naturally, know where you’ll go for fertility treatments if necessary. If you’re hoping to conceive biologically, think about whether you would also be open to adoption or fostering. Sometimes, remembering that you have other options — and that a negative test result isn’t a dead end — can help you stay optimistic from one month to the next.

Over-the-counter tests you can take at home are an ultra-private and convenient way to get a quick answer to the question, “Am I pregnant… or is this just a food baby?”

But even if you are actually pregnant, that drugstore test might not give you the right result.

Everything from medications to medical conditions to the time of day you take the test can mess with that positive and negative sign. The only way to know for sure is to head to your doctor’s office and get a more foolproof result.