What Causes Light Bleeding And Menstrual Pain Without Having Periods?

Hellow doctor! Before i had sex and experince light bleeding (with sometimes very pain on my lower left abdomen that day the pain take about three to four hrs i even fall asleep with thaat pain so i dont know when it stops,) two weeks after then i thought it could be implantation bleeding then i had to check the pregnancy test but it was negative, after two weeks i was again having another light pinkish light bleeding but it was a little bit more and some thing like little blood cells( small piece of meat or liver coz i tried to break it with my hands but is was not getting broken) then i suspect it could have been either miscarriage coz i take another pregnancy test myself and it was again negative and at this point all of the pregnacy symptomps disapeared.i had another sex day 15 after that bleeding with my new boyfriend and today is 12 days after that sex and now am experincing light bleeding in tissue it doesnt even go to my pad) which is different from the first two ones they were going to pads) me and my new boyfriend we are trying to make a baby. And this time light bleeding is having almost completely period pain but not strong. What could my situation be?