I havent had my period for 4 months?

I am 14. i got my period last year November. it was nvr rlly regular but i knw tht its gonna be abnormal for a while. i would get it anytime between half a month to a month and a half after my latest period. but i had my last period in the begining of august. that's FOUR MONTHS! i didnt so anyhting so i cant be pregnant. but what else can it be?