Painful orgasms are also called Dysorgasmia. This is a condition that occurs for a variety of reasons that may not be very clear. This is because the pelvic muscles contract during an orgasm and for some women, this is painful. These women develop painful cramps in their lower abdomen during or after orgasms. Apparently, sex isn’t enjoyable for them because of painful orgasms. Sometimes, these painful orgasms are from :

A Muscle Spasm which is an involuntary contraction of the muscle that causes a great deal of pain in the body. In men, muscle spasm is also a cause of painful orgasms. However, men who have gone through prostate cancer surgery also risk having painful orgasms during sex. This pain may create a burning sensation in the perineal and lower abdominal areas of the body.

At other times, painful orgasms in women may be caused by:

Hormonal Changes: which stems from the use of birth control pills. These pills contain lower amounts of estrogen (even less than 20 micrograms). And this explains why some people have painful orgasms.
Menopause: It should be under hormonal changes though. Women who are experiencing menopause sometimes have painful orgasms. This is because at the menopausal age, they have pelvic pain during sex when estrogen production reduces.

How Can it be Treated? See Here