I had unprotected sex with my fiancé on Friday 02/19, and I've been on birth control for over a year without never missing a pill. On Friday night I started having a terrible sore throat, and on Saturday I came out positive for strep throat. On Sunday 02/21 I started penicillin. Now I know that I have to use a backup method until I've been on the pill for 7 days after finishing my antibiotics, but I'm worried about the sex I had 2 days before I started penicillin. Since my birth control might be affected, and sperm can last up to a week inside the body, could I still get pregnant from that sperm? I'm on my third week of pills. Should I skip the placebo week so I don't have a chance to ovulate? I'm guessing Plan B would be affected as well so I wonder if it's even worth taking it. Thanks for any reply!