Period Clots and Pain

So today I thought I may have been getting a UTI. I was uncomfortable and it was hurting to pee all day. But I was in bed and I when to the bathroom and I “started” my period but I started passing these huge blood clots and the pain was just horrible. And the pain is continuing to become more and more unbearable. It’s like a cramp but it burns and it’s almost unbearable. Pamprin did nothing for the pain and heating pad isn’t doing anything for it either. May go to emergency room if it doesn’t stop.

What should I do?

Has this happened to anyone else?? Please tell me if it has.