Allow me a moment for my public service annoucement....
Until you are in a relationship with someone who's phyically health is determinded by a doctor, you should use STD-protection if you want to engage in a sexual relationship with that person.
Also, if you have unprotected sex, get the morning after pills from your doctor. (They're legal in Canada, assuming legal in the US). They are 4 pills, very inexpensive (again, here they are). Some people they make a little nausous, some (like me) end you in the bathroom for 2 days hanging over the toilet. But, it's better to do that, then face the stress anf decisions of an unplanned pregnancy.
Now that's over...
Msk is so right. I don't know how many women I've met who said every month "I KNEW I was..." and weren't. I've met women who stressed about not being pregnent so much, that they missed their periods for a couple months and developed swollen bellies, morning sickness, etc.
Take an early detection pregnancy test. If it comes up negative, go buy yourself some chinese food and a bottle of wine (or ginger ale), pour yourself a bubble bath, light some candles and pretend you're the Queen of an empire, surrounded by man servants. Well, after a scare, you'll probably won't want man servants...OK, scratch them out the of the fantasy.
FC, hugs. I've had scares and they are enough to make you go crazy, I know. Keep your mind as busy as possible, so you don't stress.
Let us know.