Passed large blood clot — what do I do?

I’m on day 4 out of 5 of my period. I’m 9 months PP. This morning I woke up to realize I had completely bled though my bad overnight. I got up, was a bit dizzy at first, went to the bathroom & when I was going I felt something pass. When I stood up I looked to see & it was a large clot that covered a good portion of the part of the toilet where the water goes down. Definitely larger than a quarter. I thought it was maybe a bunch of smaller clots that just went down there by themselves so I flushed & it was all one piece. My flow is a lot heavier than normal.

Do I go to the ER do I call my OB/GYN?