I don't think every single antibiotic will interact with birth control, but I know that some do. The doctor/pharmacist will tell you if that is the case, but since you got it from your dad, that wouldn't apply to you. Don't worry too much about pregnancy til you know more. If I were you, I would look up the medicine on the internet, and see if you can find a list of drug interactions, or call and ask your doc. Good luck, and let us know what you find out.

Be careful taking antibiotics when they aren't prescribed to you.. Plus they do no good for a cold, so you shouldn't have needed to have taken them anyway. There is some research to say that antibiotics can lessen the effect because they reduce how your body absorbs the hormones in the meds, so the bc becomes unreliable. Like it was said, this can depend on the antibiotic and doesn't always happen. It's always safer to be on a backup protection method when on antibiotics. The thing with you though, is that if you were in the "off" week, the antibiotics wouldn't have affected your birth control because you weren't taking in any hormones at the time. Therefore you would have still been protected at the time. If your period is still "off" next week, maybe ask your doctor. Being sick can sometimes mess you up too...