... taking amoxicillin for a 7.5 days and my proestrogen birth control MonoNessa at the same time. It was supposed to be 2 pills twice a day and then on the last day just 2 pills in the morning which I did. I took my bc everyday around the same time, I always do. Two/three days later my boyfriend and I had unprotected sex and he pulled out before ejaculating. Is it true that this type of birth control isn't effected by antibiotics? Also how long does it take for antibiotics to wear off?