Dark red blood

Hi I had sex Wednesday an Thursday night  and on both occasions I've bled a little but in the day there's no blood not even when I wipe ! Last night after having sex i got off my partner and he had dark red blood on him from me , I went an cleaned myself up , then this morning I went for a wee wiped and there's hardly no blood on the tissue 
Anybody have any ideas to what's going on ? My periods are regular as clockwork and I'm not due until 3rd/4th February