I had sex last week on the last day of my period. I recently (last month was the first month) started taking birth control pills, but I was also taking antibiotics (which I know can reduce the efficacy of birth control). The boy did not ejaculate in me, but he was not wearing a condom. What are the chances that I might be pregnant? I am experiencing breast tenderness, but I also know that this is a side effect of taking birth control.