What Causes Pain During Menstrual Cycle?

im in unbearable pain im on my period now day2 and the pain is so intense . last july i had ploypips removed from the wall of my womb and a dnc . i feel sick with the pain just like labour and have taken pain killers paracemtol and ibuforen . i have lost some clots of blood my iron levels were low 6months ago and was put on iron tablets for 6months which now im off .i feel weak . i also taken some like acid tablets that the doctor gave me for the heavy periods . should i ask to be refered back to the hosiptal. this cant be right .