Am I on my period or am I pregnant?

So I had sex on September 10 and about a week later after feeling weird I found out I caught chlamydia and was treated with the antibiotic that same day I threw up which was one of the side effects of the medication and now it’s October 15 and I have been bleeding for maybe 5 or so days but I’m on the pill (84 day pack) and am not suppose to have my period until October 29th. I’m not sure what’s going on but this has never happened to me.