Help! Miscarriage?

This is going to be long-ish, so thank you if you read the whole thing.

I have PCOS which means I have irregular periods. Sometimes they're 3 days, sometimes 7, sometimes light, other times heavy... so I really don't have reliable patterns. However, they are typically on the same-ish schedule, usually around 3 or 4 weeks apart.

I had sex a few months ago. After that, I went like two months without a period. I didn't take a pregnancy test at the time. Then, I started my period a couple weeks ago. It started with normal flow, lasted around 7 days and went down to just spotting. I thought it was ending.

But then it came back in full force. When that happened, I took a pregnancy test that came back negative. The bleeding was SUPER heavy at this point and lasted an additional 4 days. It also came with a bit of clotting coming out occasionally, which isn't necessarily abnormal entirely for me, but is uncommon.

It seemed to end a few days ago and I was having only very, very light spotting every so often. However, today it came back in full force... again. Super heavy. And I had a BIG clot a few minutes ago. At least bigger than I'm used to. Wish I had taken a picture, but it was the width of my big toe and the length of a french fry.

I have also had cramping pain in my left side for the past week. I chalked it up to a UTI but now I'm wondering differently.

Any ideas what's happening? Is this a miscarriage, or just extreme symptoms caused by PCOS?