Bleeding between periods

I could really use a bit of advice here, ladies.

My next period isn’t due until another 16 days. I felt a bit wet down there and went to the bathroom to check and my panties were soaked with blood and there was a huge mass of tissue on it, about 1”x3” and the blood was really dark. I just sat on the toilet and a passed a fee more clots. This is a little worrying. I do have PCOS, but my periods have been normal (3-5 days, average bleeding, monthly) for the last year and a half or so (working out and eating better). I’m not pregnant, that I know of, nor was I trying. Should I go see my gyno? Or is this normal? It certainly isn’t for me.

Thank you all.