Not sure what this is..HELP

Jordan

I started my period last Thursday. Friday and Saturday I had horrible cramps (I haven’t had cramps like this in 5+ years). On Saturday afternoon I passed what seemed to be a clot. The clot was a fleshy color. I know I’m not pregnant, my obgyn order a HCG blood test to make sure, of course it was negative. But what could this be!?