Help! *TMI* Large piece of thick tissue came out of me during period

I had laparoscopic surgery in July 2019 for endometriosis.

I've had 2 heavy periods after it. Then I started the birth control Seasonique as suggested by my surgeon (runs for 3 months at a time, means I only have 4 periods a year).

I've just started my first period on Seasonique a few days ago. I was in the shower today & got bad cramps. I took my tampon out when I stepped out of the shower. I felt blood coming out so I wiped with my towel and saw this!

A large piece of very thick, tough skin. Covered in blood. I dont know if this is normal? I dont know if this is from surgery? Or if somehow the odds have been against me and I've had a miscarriage?

Any thoughts?