V.P.
Antibiotics can affect the pill. You may want to ask your doctor what you should do -- it's possible to get pregnant that way, and if you are, you may not want to be taking the pill. It's also possible that you're simply spotting because that happens to some people on the pill -- you haven't said how long you've been on that pill -- and the fact that you were taking other medications could have affected the pill in a way that caused breakthrough bleeding.