Hello,, pain during menstruation Is called dysmenorrhea, some women who are sensitive will feel all the during menstruation, but if it is associated with any other symptoms like white discharge, fever, very severe pain, passage of clots could be because of some infections (white discharge) or fibroid uterus (clots +pain) or polycystic ovarian disease,(severe pain +weight gain +android symptoms). Consult a gynecologist to find the cause and to treat you.