This study will examine pelvic pain associated with endometriosis and explore better approaches to treatment. In women with endometriosis, uterine tissue grows outside the uterus. Standard treatments - altering hormone levels to prevent endometrial tissue growth or surgically removing endometrial tissue - treat pelvic pain only temporarily. This study will investigate the role of sex hormones, immune chemicals, stress hormones, and genes in pelvic pain and determine how the nerve, muscle, and skeletal systems are involved in this pain.