What kind of birth control are u using? Lets Say im assuming the pill the effectiveness is 97% which theres a chance u can get pregnant by 3%...and If ur taking antibiotic it will definetly loose the effect of birth control & can get u pregnant. Hope this helps but definetly abstinence is 100% preventable ;) good luck.
Have you missed your period yet? That's really the only way to tell unfortunantly :( but just wait it out. I am 20 and I was pregnant in July for 9 weeks before I miscarried but when I foud out I was pregnant I just "knew" as weird as that sounds. You know your body more then anyone if your scared some test tell you 5 days before your missed period. Don't stress though to much because it can cause you to miss your period. And ignore the comment about your only 15 it's your choice I lost mine at 15 as well. But just remember be smart about it with STD because I know you already know birth control doesn't protect against STD's but at 15 I didn't think I could get one.. Luckily I didn't but it can always happen. So just be careful :)
First of all you are 15 and really shouldn't be sexually active at your age, birthcontrol does not protect against STDs, and is not 100% effective on preventing pregnancy. Also symptoms mean nothing, the only way you can tell if you are pregnant is by taking a pregnancy test after you have missed your period.
It all depends some bc take a few months to actually kick in. If you feel different and think something is up i would take a test or maybe call your dr and talk to them about your concern