Im confused

So for months now my period is soo strange. On the day it starts the first thing i notice is some light spotting, then I'm having the worst cramps ever like I'm giving birth :D and out comes a biiig lump or what of blood. It's a size of my thumb than i have some more spotting and that's my period done. 2 days and it's gone. Anyone else has something similar? What could cause it?