what causes period pains?
Menstrual cramps may be caused by:[5] 1  Endometriosis: The tissue that lines your uterus becomes implanted outside your uterus, most commonly on your fallopian tubes, ovaries or the tissue lining your pelvis. 2  Uterine fibroids: These noncancerous growths in the wall of the uterus may be the cause of pain.