Well, I'm not as young as you are, mom1978, but here's what works for me. I take a tablespoon every day of flax seed oil with evening primrose oil. It totally took care of the problem for *me*. Barleans is the brand which has those two in a combo formula called Omega Twin. Since you have CD, if you decide to try it I would start with a smaller dosage (1 tsp. maybe) and gradually increase making sure it doesn't cause you any issues. It really shouldn't, though.
As for the cause... It's probably just those lovely hormones gone wacko...
Here's what an alternative website says about
evening primrose oil:
"Relieves the discomforts of PMS, menstruation, endometriosis and fibrocystic breasts: By interfering with the production of inflammatory prostaglandins released during menstruation, the GLA in evening primrose oil can help to lessen menstrual cramps. It may also minimize premenstrual breast tenderness, irritable bowel flare-ups, and carbohydrate cravings, and help to control endometriosis-associated inflammation."