It ok to have sex when done with antibiotics while on birth control?

I was on antibiotics and finished them. I had sex after taken them on birth control and take it like normal. We didn't use protection. after a week, I started to feel like i was getting my period a little earlier?Does this mean i might be pregnant or just because of the anitbiotics? or is it stress, cuz im plannin my wedding :) and lookin for houses?