Taking amoxicillin on3rd day of taking it had unprotected sex i'm on bc and breast feeding my6month old cycles have not returned chances of pregnancy?

Pregnancy?: The risk in your case seems low, but the chance is always there. If you think you may be pregnant get a home test kit and use it. If negative you may want to wait 10-14 days and retest. These are relatively inexpensive.

Very low!: I never make guarantees, but your chances of pregnancy are extremely low. Although antibiotics can reduce the efficacy of birth control, between the fact that you are breast-feeding and not menstruating yet, your chances of conceiving are slim. If it has been less than five days, you can take Ella (ulipristal acetate) (rx morning after pill) to be safe. And be sure to take a pregnancy test two weeks from the event.