Hi. Me and my boyfriend are currently 17 and we're not trying to get pregnant. I know it was irresponsible but we had unprotected sex he came inside of me I told I was on birth control (which I am) but I am also taking an antibiotic called sulfamethoxazole. So he got me plan b the next day I am really worried can someone tell me if the antibiotic prevents the birth control all together? HELP PLEASE I NEED ANSWERS :(