What Does A Large Mass In The Uterus Indicate?

I had a c-section jan 25th and the end of feb the doctors discovered a large mass 8 centimeters large in my uterus. i had two ultasounds done and they discovered it was a blood clot. the one doctor told me that it could be 3 months before it is completely passed. yesterday i had a large mass come out of my vagina it wasnt blood. i think it was tissue, it was white and it was a little larger than a quarter. i called the doctors office yesterday at 12:30 and no one ever called me back yet. i had a lot of complications during my c-section. i had placenta accreta and i lost a lot of blood during the c-section. i had i believe they said 12 doctors in the operating room and a team of doctors on standby. could the tissue be the blood clot?