literal CHUNKS out of me

I usually have bad cramps during my period and at random times throughout my cycle. I have super heavy periods, which equals a whole lot of clotting. BUT, the other day when my period started, I was at a restaurant with my mum and all of a sudden started feeling these ridiculously sharp pains in my lower abdomen and anal area. They felt like horrible period cramps plus very sharp, sudden pains. I tried to get up but couldn't walk and had to sit back down in the restaurant and clench my teeth together so I didn't scream. 

I waited a few minutes until the pain subsided to go to the bathroom, and about 30 seconds later,  it started again. I crouched down trying not to scream (unsuccessfully) for about 5 minutes. Then it went away again. 

For the rest of my period, I was clotting very badly and chunks of.. tissue came out of me. I looked closely to make sure it wasn't toilet paper or anything. It was actual chunks of something.. like fleshy tissue. Has anyone experienced anything similar? 

Note: I have PCOS but it has always been quite mild. I have regular periods, and they're very heavy and last approx 6 days.

I'm sexually active but have had 2 periods since I've last had sex. 

I have booked an ultrasound and blood test for next week but I'm stressing out! 

Any ideas?! 

Thanks ❤️❤️❤️❤️