What Causes Stomach Cramps And Abnormal Stools During A Menstrual Period?

I am on my period. Today I have had REALLY bad cramps from about 3:30pm to 6pm. When I went to use the restroom I potties out this jelly fatty thing (it kinds looked like a bloody tampon that had been soking in water for a while...I know that sounds weird). After I had done this my cramps stoped. Do you know what that could be? Should I go see the doctor?