What should you do if you 15 and dont have your period for 4 months and not sexual cative. can it be some dise?

Im 15 I use to have period every two month. which mean 6 time a year bt now i have benn on 4 months and never have it. and im not sexual active. bt i have aoll those pregnancy sign dizzy hungry every 30 minutes, fainted, throwing up, have backache and always sleepy.