Possible miscarriage

So my period was 2 months late, and I finally got it. When I did the pain was unbareable in both my stomach and my back. I also bled very heavily which worried me, along with that was tissue about the size of a thumb wayyyyyy too big to be a clot. which was evidently the embryo.
​I'm pretty sure all tissue has gone now but I still think I should visit my gp. What would they do to confirm a miscarriage?