Help! Possible pregnancy?

So I’ve been taking birth control pills and I got sick so I have been taking antibiotics. I know antibiotics basically stop the powers of the BC. So I got my period on Sunday (one week in from taking the antibiotics) and on Saturday morning I had unprotected sex and he came in me. I haven’t started my fertile window yet. How likely would you say I could get pregnant from this? I didn’t take a Plan B either because I didn’t think about it until now.