My Period Is Usually Heavy And Lasts 3 Days. Tuesday

My period is usually heavy and lasts 3 days. Tuesday it started as spotting and Thursday got heavier, Friday the cramping was so intense and I felt like I had to push something out. Went to bathroom and there was something that looked like tissue on the tampon. Put on fresh one, stood up and blood was so heavy it flowed down my leg, removed it wiped and sobbing clot that looked like tissue with come black spots in it was on the tissue. Bleeding had slowed and so has cramping. What could be wrong?