I am clueless.. Can anyone tell me if this is a possible very early miscarriage?!

I have been trying to get pregnant for ages (3 1/2 yrs). I have thyroid problems, endometriosis and pcos. I’ve had big rounded clots for years (like golf balls) with periods but this is different. This is tissue with tiny dark red unusual shaped clot type stuff inside. It has happened a few times when I’ve had an unusual amount of blood loss (when a period comes out in one big go rather than the usual 6-8 days, it’s more like 3 days), horrible severe back pain, dizziness and nausea. I don’t know what an early miscarriage looks like but wanted to check if it is possible this could be one? Any advice or information appreciated. Thank you x