Hey- I'm 19 and know how you feel. When you start having sex for the first time everything can make you paranoid. You really should consider birth control of some sort. It is good that you use condoms, but if one should break you'd be right back where you are now. I take the pills, but often times miss one or two so I am switching to something more consistent for me. If you think you may also be forgetful, look into the patch or something. I don't know how old you are, but also if you are going to have sex you really should be going to the gyno to get your BC as they can better help suit your needs ( I had to switch brands several time due to migranes). As for right now, try not to worry too much (I know it's hard) and just try to wait for your period. Stressing yourself out can make your period late and then you just stress even more. The chances of a normal couple trying to get pregnant is only something like 25% anyway, so what are your odds? Possible- but not likely. Hope I helped a little.
Try not to be afraid, stress in this situation doesn't do anything but make you more tense, and make it more likely you will feel different or your period will be irregular. :) It sounds like you are pretty safe, but really there is no way to be sure except to wait and test. There are other reasons besides concerns about pregnancy to be worried, as STDs and infections are passed through unprotected sex. So do take care of yourself in every way. No more sex without at least a condom, and if you can get on birth control pills all the better, because condoms have less than perfect success rates. Good luck, sweetheart.
If you're going to be sexually active and do not want to get pregnant than you should really use protection everytime -- and you should think about going on the pill.
If you go to an OBGYN, have her/him prescribe - you can also go to a Planned Parenthood near you & have them give you the pill.
There's always that chance that you can become pregnant after unprotected sex & the guys pre-c*m has sperm also - the pull-out method is not 100% safe.. take a HPT to be sure....
good luck