Bleeding That Extends Long. Bad Stomach Cramps And Back Pain. HPT Positive. Why Did I Get Period?

Hi whenever I have a period it goes for 3 days then stops for a day and then starts again for 2 day and then I m finished I am very regular however last month I had a funny period. I had a lot of pain (which is common) when my period did start it was heavy and lasted for two days and stopped as usual but it did not start again. I had sex on Sunday (which was 2 days after my period had finished). I then had bleeding which was only bright red on Monday for one day. Because I have already lost one of my ovaries and tube I am careful about checking if I am pregnant. I had taken a HPT just before my period started and it was negative. I then took another one 2 wks later because of the strangeness of my period and it came back positive, I did another one using the clear blue line brand it said 3+ I am having my period right now it s not heavy at the moment but it is bright red and I am having some slight cramps which are usual for me (usually I have really heavy cramps in my stomach and back). I just took another HPT 2 days ago and it was still positive but I am concerned because i have just got my period.