Help??

So, I've been having unprotected sex with my lover for the past month and the most recent time ( week before last ) he got some inside me, when usually he pulls out. This Monday my period started and bled heavy for two days then stopped on Thursday and now there's creamy orange discharge and occasional blood. Usually my period is entirely regular so now I'm concerned. I had a pregnancy test done at the doctors on Monday and it was negative. What could the spotting and discharge mean?