Stopped taking the pill and had sex last weekend with out contraception and my period is not here yet could this be because i'm on antibiotics?

Probably not: I do not think that antibiotics would influence periors. However, after stopping the contraception it could reusult in a delay before you regulate.

So many changes: You mention so many things, it's hard to say which is affecting what. How long have you been off the pill? Have you had a period yet off of it? Why were you on antibiotics - sick, STD? These too could affect timing of your period. You also had unprotected sex - you could be pregnant. So start by taking a pregnancy test if it's time for your usual period and repeat in a week.