So my girlfriend has been on the pill for like 4 years. She is now on week 2 of her birth control. She just finished a whole bottle of antibiotics 3 days prior, for a sinus infection. The bottle nor doctor said a back up method of birth control was necessary. We had unprotected sex last night, but we keep researching that we were supposed to wait a week to a month before relying on the pill again. Any input? Thanks.