Still miscarrying months later / incomplete miscarriage

I had a miscarriage in Feb at 8 wks - bleeding lasted 10 days, then my cycle started 6 weeks later. I had two perfect cycles, my period was 28 days and right on time. I had negative pregnancy tests throughout this time and even positive okp's. 
This last cycle I had terrible cramping beginning a week before AF was due which isn't normal for me. AF was 3 days late, and felt like a lot of pressure. I went to the bathroom and actually passed large grey tissue without blood. Then AF started right after and was heavy. 
I believe this is the last of my miscarriage, but couldn't find much online about a miscarriages that last months. I'm almost positive it wasn't a second pregnancy because I take HPTs like there's no tmrw! They're always negative.
Have any of you had this experience, where your miscarriage "finished" months later?
I'll call my doc tmrw but would like to hear any of your experiences.
Thanks so much ladies.