i think you should see a doctor ASAP
Talk to your physician about doing a blood test. Antibiotics definitely decreases the effect of birth control. So if you are not trying to get pregnant yet, use condoms if your are being treated for anything involving you taking antiboitics. It's not a bad idea to use condoms along with birth control whether you are being treated with antibiotics or not. Until you've reached a point in your years to come when you decide it's time to get pregnant, protecting yourself from STD's and staying healthy, will make that moment less stressful for you.
i am 16 and this is what happened to me i had sex and missed my period but the tests came back negative for a while, but i am pregnant. and i stopped my birth control as soon as i thought i was. but i am pregnant so i think that you should wait awhile. but dont stress about it because if you do you chould convince your body you are. i know its easier said than done but dont stress yourself out, because if you are its not good for the baby.
In order for a pregnancy test to be accurate, you have to take it at least 2 weeks after having sex. If you want to, take another test in a few days. If it's negative, then you are not pregnant.