i'm sixteen. I havent had my period in around 5 months. I've never had sex, so it cant be that. But, i play volleyball and im pretty active. I've been getting my period since 8th grade. This past summer i was stressing a lot, so i lost around 7lb's, but i put all that weight back on and now im around 110lb's. Some people say it's because im active that i haven't been getting my period, and im pretty thin too. Is this something that is serious? and should i see a doctor?