Other possible causes of the pain (though less likely): kidney stones (if you have a positive personal or family history of kidney stones or sludge), ovarian torsion (the ovaries twist around themselves which interrupts blood to them thus the pain,tthen untwist so pain goes away), or even dysmenorrhea (pain related to the menstrual cycle).
You should definitely get a culture of the vaginal discharge in addition to a proper pelvic exam to rule out PID. During the exam other causes will also be ruled in or out. Additional tests that should be done include a complete blood count, urine analysis and culture (to rule out urinary tract infection). If you turn out to have a sexually transmitted infection (STI) like Neisseria, you need to inform your sexual partner so that they get tested for the infection and receive antibiotics..