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We've all been told that sex isn't supposed to hurt—but in reality, sometimes it does, and it could be for a variety of different reasons. If you reached orgasm during sex, you may experience some cramping in your uterus afterward. "The act of physical contact or sexual activity releases oxytocin, and that causes uterine contractions," says Jennifer Ashton, MD, a board-certified ob-gyn and cohost of The Doctors. If this cramping only happens once in a while, it's nothing to worry about, says Ashton. But if the pain starts interfering with your sexual behavior, you should see your gynecologist, since regular pain after sex could be a sign of endometriosis, fibroids, or even ovarian cancer.

You feel the burn.

Don't freak (yet)—that burning you feel during your post-sex bathroom excursion probably isn't some scary STI. "There can be some engorgement of vaginal tissues, and since the urethra is so closely situated to the vagina, that can cause temporary burning or stinging with urinating after sex," Ashton says. But here's the thing—this burning or stinging should be temporary (and very, very brief), so if you're still experiencing some discomfort hours or days later, you could have something more serious on your hands.

You got a little something on your sheets.

We're talking a little spot of blood here or a little dot there—nothing Carrie-esque by any means (that would be a definite sign to see your gyno—or even the ER). But the fact is, gynecologists see instances of bleeding after sex quite a bit. "The most common cause would be an inflammation of the cervix that gets contracted during sex," Ashton says. The vagina can also tear just a little during particularly rough sex or even when you change partners (especially if there's a size upgrade involved). The blood coming from an inflamed cervix or vaginal tears is normally bright red, but if you see some darker blood, that's not immediate cause for worry, either—it could just be some old menstrual blood coming from your uterus. That said, if any type of postcoital bleeding happens more than once, a gynecologist should take a look.

You've got an itch that needs scratching.

If you're fidgeting around, trying to scratch an annoying itch after getting busy, it's likely that you have a sensitivity to a lube, gel, or even condom that you just used, says Alyssa Dweck, MD, coauthor of V Is for Vagina. But if you haven't introduced any new products into your nightly routine, you could be allergic to your partner's sperm—or more specifically, a protein found in sperm, according to the International Society for Sexual Medicine. Symptoms usually start within 30 minutes of contact with semen and can last anywhere from a few hours to a few days. Even more confusing, a sperm allergy can arise anytime, whether you're new to sex, you've just recently switched partners, or you've been with the same person for years.

You could really use some alone time.

Cuddling after sex is normally a given, but sometimes that extra snuggle time is the farthest thing from your mind—and that's more common than you think. According to a recent study in the journal Sexual Medicine, feelings of depression, anxiety, agitation, or aggression following sex are known as postcoital dysphoria (PCD) or "post-sex blues." Findings showed that 46% of the 230 women polled for the study experienced PCD during their lifetimes, with 5% experiencing PCD symptoms a few times within the past month. Researchers believe PCD isn't linked to overall sexual function, but it could be more common in women who are more "emotionally reactive" (like those with anxiety surrounding their relationships or those who have difficulty maintaining their personal lives when coupled up).

ou make a beeline for the bathroom.

In addition to making you itchy all over, your guy's semen could also be giving you the post-sex runs, according to this article by Women's Health. A chemical compound found in semen can cause cramping and diarrhea when introduced to the vagina and colon, says Teresa Hoffman, MD, an ob-gyn with Hoffman and Associates, a group affiliated with Baltimore's Mercy Medical Center. (Learn what your poop says about you.) Here's the gist: Those compounds (called prostaglandins) cause smooth muscles to contract (like the ones in your uterus and intestines). And when those muscles contract too quickly, well, get thee to a toilet, ASAP. Luckily, there's a quick fix: Make him wear a condom—that way, his ejaculate won't get anywhere near your rear.