Could I be pregnant?

Ok so about three weeks ago around September 5th or 6th my bf and i had protected sex. Everything seemed fine and it didn’t seem like the condom broke. I’m not on birth control yet though. My period came on time on the 11th and it was normal if not a little bit heavier than usual. I thought I was fine but this week I’ve been feeling somewhat nauseous and have lost my appetite. I worry a lot so is there a chance I could be pregnant even though I got my period afterwards? Thanks.