Passing Large mass of tissue two weeks PP

Ana
***graphic detail warning***I delivered a healthy baby boy on September 11th. Delivery went well, it was a vaginal birth and I felt great afterwards (minus the 12 hours of a Catheter because my bladder was dangerously full after delivery). Until this past weekend I started getting deep vaginal aches that were so bad I couldn't stand for more than a few minutes at a time without having to bend over or find a seat. Then, last night after having had minimal bleeding that was tan in color for the last few days the flood gates opened. Blood was trickling out of me and I lost several large clots. I was soaking through a pad every 30 minutes and by the time I got to the ER it had soaked through my pad, shorts and was all over the waiting room seat. My temp was 99.6 which is above normal for me but not technically a fever medically. Since the bleeding started I had intense contraction like craps but super low and I felt pressure around my vagina and even rectum. No one in the er seemed too concerned about it so I kept calm. The pushed on my tummy and felt around and commented on how full my bladder felt. After urinating in the bathroom I lost some more clots and then suddenly this large mass of light grey tissue (I think?) came out of me. It looked like a brain and felt heavy and dense. After that they did an internal ultrasound and said everything looked fine. I told them about the mass that came out and that I saved it in the bathroom and they said no need to save or look at it but that I was good to go home. Since passing the mass my pain is significantly decreased, the pressure is gone and the crazy bleeding has minimized to normal postpartum bleeding. So what the heck did I pass?!?!? Part of the placenta? Don't they check those though? I took a picture but didn't want to post it and freak everyone out. Any advice or knowledge would be helpful!