White tissue like stuff 4weeks and couple days postpartum...

Hey, I stopped bleeding a few days after baby was born, than started again and stopped, started, mostly spotting, some times a little heavier ,so on and so on. About a week ago my left side was hurting but stopped a couple days later. Today I started bleeding a little more again and was a little crampy this morning on and off. When I went to the bathroom there was a clump of whitish tissue like stuff with streaks of mucusy blood in it and it all floated. It was like the white tissue stuff I had at the begining of most of my pregnancies with bleeding (babies were fine though) but havent noticed the white stuff with my last couple of pregnancies. The doctor said with my first two pregnancies they thought it was part of the cyst you get at the begining of pregnancy. It looks like the same thing that I had than. Does anyone have any ideas. Please note that I have had unprotected sex since baby was a couple days old. But I have with ALL my babies after birth and never got pregnant than. I never had this white tissue post partum before either. Please HELP!!!?? Thank you and have a great day...