Why my 17 year old doesn't get her period anymore?

i know for a fact she is not pregnant! i don't remember what pill she was on. it was a way's back. my daughter is on the heavy side. she's not as active as she should be but as of now she is exercising.once a month she'll get headaches and feel like she's going to start. she even get's cranky. but never start's. Doctor's wanted blood done and that came out ok. but now she has a appointment with the obgyn. they said there going to look at her overies. when she was bleeding for that long period of time all they gave her were those pills. i think they were regular pills. i had my period every 3 to 4 month's when i was her age. i took regular birth control pill's and that helped alot get back on track, but for her it dried her right up and never saw another one again. what would be the next step for her ? she's really nervous to go to the obgyn. she's never been so would they beable to do anything else besides a pap? if it came down to that?
thanx a whole lot.