Will antibiotics mess up my period?

I've been very regular since I started my birth control pills about two years ago. However, about 2 weeks ago I was given very strong antibiotics to help with my Gastritis and H Pylori. My period was due Friday and I've only seen very light spotting. Light brown and very little red. My partner and I had sex only a few times. The first time we did it this month was October 16th. The last time being Thursday, October 26th. We used a condom every time we did it because we know antibiotics can cause birth control pills to fail. I am scared because the spotting is here in place of my new period. Is this implantation bleeding or did my antibiotics just mess with my cycle? Please help!