Stacey Missmer, et al. “A Prospective Study of Dietary Fat Consumption and endometriosis Risk.”
It can be due to any number of treatable causes, like endometriosis.
endometriosis en·do·me·tri·o·sis (ěn'dō-mē'trē-ō'sĭs)
A condition, usually resulting in pain and dysmenorrhea, characterized by the abnormal presence of functional endometrial tissue outside the uterus, frequently as cysts containing altered blood.