uterus lining (tissue?) fell out NOT near period tmi picture

Okay, so I'm NOT on my period. I'm on birth control pills and it's not anywhere near my period break. So, yesterday morning my boyfriend and I were doing oral and he fingered me (kind of aggressively I guess but not noticeably). But when we were done I bled a little on his chest. I'm not a virgin or anything so I assumed it was kind of just rough or maybe I got a cut. But then all day it was lightly painful all day and bleeding. At the end of the day I went to go pee and it felt weird like when a blood clot is coming out and what I think is thick uterus lining fell out of me. But it was pretty big and felt/looks like flesh or tissue. My stepmom (who's an ER nurse) said it was super weird and we went to the ER and the dr basically just did a pelvic exam and said I had no infection etc so to just see my gyno next week. Today it was still painful and bled lightly. I'm just wondering if anyone has any experience with this??? I've had bad blood clots before but nothing like this and I don't understand why any of it happened? Could it be from a cut from his fingernail??

THANK YOU to anyone who can help me :)