I was on a amoxicillin for 5days. had bleeding so started placebo pill 4days later.took 7. had sex on first active pill on new pack. risk of pregnancy?

Very low!: I never make guarantees, but your chances of pregnancy are extremely low if you have not taken off more than 7 days of active pills. Although pharmacists often say that antibiotics can reduce the efficacy of birth control, the studies were done on a different type of antibiotic (not related to Amoxicillin), and no other studies have had the same conclusions. I wouldn't worry any more than normal.