Pelvic pain that occurs in a pattern of increasing and decreasing intensity is considered a "cramp". Cramps may be caused by a number of conditions. The relationship of the cramps to the menstrual cycle helps your doctor determine the cause of your pain.
Cramps that occur with the menstrual cycle (dysmenorrhea) can be caused by an obstruction or narrowing or the cervix, growths within the uterus (polyps, fibroids or myomas, or adenomyosis), endometrial or uterine lining tissue outside of the uterus (endometriosis), or for no discoverable reason (idiopathic).
Cramps that occur in the middle of the menstrual cycle (Mittleschmertz) are due to the opening or rupture of the normal ovulation cyst. Sometimes there will be more fluid in the cyst than is average or the cyst will open near a blood vessel causing more bleeding than average, resulting in pelvic pain. This pain usually lasts from a few hours to 1-2 days.
Cramps that are unrelated to the menstrual cycle may be related to an infection, bowel problems such as constipation, diverticulosis, or food allergy, or scar tissue in the pelvis.
Your doctor will use a combination of your history, physical exam, and lab or radiologic tests to determine the cause of your cramps. Sometimes a surgery such as a hysteroscopy or a laparoscopy will be needed to determine what is causing your pain. Once the cause has been determined you and your doctor will be able to go over the options for treatment and decide on the best course for helping you relieve your pain.