Quoting Lady GooGoo™:" Did you have unprotected sex while taking the antibiotics? Aive never heard pf antibiotics making you bleed..."
Quoting Shonna Boyd:" its possible that the antibiotics messed up your birth control and then messing up hormones and causing ... [snip!] ... make sure nothing else is going on, because antibiotics can and do mess with birth control and have caused lots of pregnancies!"