Period is 2 weeks late!

I was expecting my period on the 12th. I did have unprotected sex back in September. On Sunday morning I woke up spotting very lightly and nothing for the rest of the day. On Monday I was spotting a little bit more and nothing the rest of the day. Today i bleed a bit more but only in the morning and nothing the rest of the day. I took a pregnancy test and I got a BFN. My period has never been this late and my breast hurt so much. What is happening and what do I need to do? Please advise.