They will give you a pelvic exam and possibly draw blood to test your hormone levels or for STD's. The pelvic exam includes inserting forceps into the vagina and having the doctor feel around to see if they notice any abnormalities plus use a cotton swab to get a culture to test for any STD's (pap smear). If you are over 18 and still have not started your period, they may do an ultrasound to look for cysts or endometriosis. I've had family members who didn't get their first period until 17-18 years of age. It was all due to genetics and endometriosis runs in my family with almost every woman, and we have a LOT of women in our family.