Please help

I had my period last month on 9/21/16 I had sex 9/28/16 I than received my period 10/21/16 we used a condom I was a couple days late it wasn't like my regular period usually I have a heavy flow & it was medium flow we used protection I still got all my previous signs that I get on my period, but you can also mistake it from being pregnant I took two test & they came back negative. Is it possibility that I am pregnant? Or is my body just adjusting to me having sex. Please comment.