I Had My Period On November 25th 2015. I Was

I had my period on November 25th 2015. I was supposed to get my period last month around the end of December but it was just spotting and usually my periods are heavy. it only lasted for like 3 days. i look it up and it says it could be implanation bleeding. i did have unprotected sex the day before my period came. im not sure if im pregnant or not?