If your health education stopped around your teen years, there’s a whole lot of important information that may be missing from your knowledge bank.

”Sex ed in your high school health class may have taught you how to put a condom on a banana and that sexually transmitted infections are to be avoided,” says Kate White, MD, MPH, assistant professor of obstetrics and gynecology at Boston University. “But it probably didn’t teach you much about a woman’s period.” Because of that glaring omission, menstruation is a topic rife with misconceptions and outright mythology. Below, four of the most common myths—debunked.

Fact: Although the chances are slim, it is possible to get pregnant if you have unprotected sex during your period. Your chances of becoming pregnant are highest right before and during ovulation, when one of your ovaries releases an egg. If you have a textbook 28-day cycle, this generally means ovulation occurs about two weeks before your next period starts.

But—and this is a big but—because each cycle is different, ovulation can seem to happen at any time, and it can vary from month to month. If you have a cycle that lasts about 35 days, you may ovulate around day 21 of your cycle. If you have a cycle that’s shorter than 21 days, you may ovulate around day seven. Because day one is the first day of your period, that means ovulation and menstruation can technically overlap.

It’s also important to remember that sperm can live inside your body for up to five days after ejaculation, so even if your egg wasn’t around to be fertilized at the time you had sex, there’s a chance fertilization could occur up to a few days after.

Think of it this way: “If you have a 21-day cycle one month, that means you’ll ovulate around day seven,” explains White. “So if the first day of your period is day one, and you think you can have a week of condomless sex and be safe from pregnancy, you might have sex on day four. But because sperm can live for five days, they may still be alive and kicking on day seven when you ovulate.”

Another thing to consider? “The bleeding you assume is a period may not be a period,” says White. “You can have irregular bleeding for so many reasons (polyps, infections), and not all bleeding is menstrual bleeding; just like not all sneezes mean you’re getting sick. People see blood and think, ‘oh, I’m on my period and I’m safe,’ but that kind of thinking can lead you down the wrong path.”

All that said, while pregnancy is still a possibility, and you should take precautions if you’re not trying to conceive, your period doesn’t have to be a dealbreaker when it comes to sex. “It’s totally fine to have sex during your period,” says White. “Some women find that bleeding adds lubrication, making intercourse more comfortable.” And while intercourse alone won’t change how much you bleed overall, White says sex may “shake some loose,” meaning you may experience a heavier flow afterward.

Fact: While the majority of women experience occasional PMS, the symptoms don’t have to have a significant impact on your life and can often be controlled with diet and lifestyle modifications. Here are a few ways to manage symptoms:

• Eat smaller meals more frequently to minimize bloating.

• Get plenty of sleep to sidestep fatigue.

• Incorporate yoga or massage to relieve stress.

Some women also report feeling better with the use of certain supplements, but there’s not enough research to back those claims. Keep in mind: Every woman is different, so what works for your sister or friend may not work for you, and vice versa.

Experts aren’t sure what exactly causes PMS, but it could be due to a few different factors including hormonal fluctuations and chemical changes in the brain. If you’re unable to manage your PMS-related problems with lifestyle modifications, you may be part of the 20 to 40 percent of women who have more severe PMS.

If the the symptoms are so intense that they interrupt your everyday life, you may be among the three to eight percent of women who have a severe form of PMS known as premenstrual dysphoric disorder (PMDD). In these cases, your doctor may be able to prescribe medications or recommend different types of therapy that can help you cope with the physical and psychological symptoms.

Fact: While some women may feel like taking it easy during the first few days of their periods, there’s no medical reason to avoid exercise at any point during your cycle. “Absolutely no harm will come to you or your uterus if you do a rigorous workout during your period,” says White.

So listen to your body. When you do feel ready to exercise, consider incorporating regular, moderate-intensity aerobic activity, which has been shown to help reduce the symptoms of PMS. “Just make sure to take proper precautions,” says White. “You may experience some heavier bleeding during exercise.”

Fact: Although a 2003 study found that the hormonal changes leading up to ovulation can occur multiple times within one cycle, the results don’t indicate that ovulation itself occurs more than once. What is possible? Ovulating more than once in a month (if your cycle is short) and releasing more than one egg during the 12- to 24-hour ovulation window—that’s how fraternal twins occur.

Typically, about 15 to 20 eggs enclosed in follicles start to mature within each ovary every cycle. The growing follicles produce estrogen, which triggers a surge in luteinizing hormone (LH). This surge causes the largest follicle to release its egg (i.e. ovulation).