Possible Miscarriage?

Kaitlyn

So I had my son six weeks ago, I’ve been sexual active since two weeks postpartum and got my first period three weeks postpartum. About two days ago I started cramping and then while at work last night I passed this grayish white tissue about the size of a quarter and started spotting. I had been nauseas for maybe half a week before this happened. Thoughts? *NOT TRYING TO CONCEIVE