Chances of pregnancy??

I am taking birth control pills. Have been for over a year now. I was being treated for a sinus infection so I was on antibiotics for 2 weeks. I had unprotected sex March 28th and today (April 3rd) I noticed I had snotty like CM. It was stretchy, kind of cream colored or white, and reminded me of actual snot out of your nose. Could it be possible that the antibiotics made my birth control pills less effective and I ovulated? Is there a chance of pregnancy? (Last period was 3/20 or 3/21 and I have 28 day cycles) please help!!