What can cause menstral cramps that are extremely painful?

Endometriosis, etc. Severe menstrual cramps can be due to endometriosis, uterine polyps, uterine fibroids, or adenomyosis. These are the most common causes of severe menstrual cramps and you should see a gynecologist for further evaluation. Cramps that do not resolve with over the counter anti-inflammatory agents are more likely to be one of the above.