If you had recurrent miscarriages, did you ever find out why?

I've had three now but because one was a chemical and I had a healthy pregnancy between the other two, my OB's office thinks I just have bad luck. My primary care doc just tested me for a possible thyroid issue but my levels came back normal. I need to have one more miscarriage to see an RE, but I really hope I don't get to that point.

I guess I am just scared that there is some simple thing I could be doing to prevent them but I'm not because no one is testing me for anything.

Just curious what the experience of others has been like.