I agree, get a test and take it (make sure you throw the evidence away outside of your house if you don't want your parents to know). Since you're on birth control, you should be fine. The Pill is something like 97-98% effective when taken as directed.
It's too late now, but if the situation arises again (hopefully not!), the morning after pill is now available behind the counter at most any pharmacy, provided you're 18. If you're younger, you'll have to see a doctor to get a prescription. Many cities have pregnancy crisis clinics you can go to for free to get a pregnancy test, condoms, and the morning after pill, or at least a prescription for it (must be taken withing 72 hours of sex, and the sooner than that, the better).
Now, the sermonizing. Like Canyon said, you can get worse things than pregnant from having sex without a condom. Remember that when you have sex with a man without a condom, it's like having sex with everyone he's ever had sex with without a condom, and everyone those people have ever had sex with, etc. In other words, it connects you to the human race in ways you'd rather not be connected! If he won't wear a condom, then he obviously doesn't want sex badly enough to warrant giving it to him. Remember that old maxim, "No glove, no love." I would go on about if you're scared for your parents to find out that you had sex, then you're probably too young to be having sex anyways, etc., etc., but I recognize that my lack of sexual experimention makes me really odd, not the norm. Heck, even our second President, John Adams and his wife, Abigail, wrote each other sexually-charged letters before their marriage (and she had a baby 8-9 months after they got married, cough, cough). Unlike the current President, I'm not going to bury my head in the sand and pretend that pre-marital sex doesn't happen and that no one has sex before they are 20, so I will just leave you with the previous message of always use a condom to protect against sexually transmitted diseases and always use BC to protect against pregnancy (because condoms are less reliable than BC on that account).
I know you are usually D, but I used to always get constipated before my period. I was never regular, so that was one of the signs that it might be one the way. While you're out shopping for a prenancy test, you may want to pick up a package of Midol and see if that relieves your bloating, etc. Your symptoms are typical of PMS.