could I be pregnant?

I thought I was pregnant but I had my period 3 weeks after I had sex....I'm on the pill but I had sex when I was on my period and he pulled out and I took my pill the next morning after we had sex because it was time to start taking it again. 
My boobs feel fine, I'm not urianting anymore and discharge is the same amount but I do have stomach pain every now and again could I be pregnant I need advice?