My last period was in June 2012, I have missed the last two months. I have done two home pregnancy tests and they where negative and been to the docs and that was negative too. However last night I had sex with my boyfriend and I have about a tablespoon of bright red blood and nothing since then? I was having sore nipples but they have calmed down still a little tender but better. What could this be I last did a pregnancy test at the docs in July.
Thanks for any advice.

Did you tell the doctor you've been missing periods? This is nothing to mess around with!! If you are not bleeding regularly, then yes, there is a problem. But it could be many things, or, nothing at all. You must tell your doctor! You didn't say how old you are, and when you started to get your periods. (All of this stuff matters!)