Im to skinny what should i do?

hey well im 15 im gonna turn 16 on feb 2nd and like i weigh 78 like omg people make fun of me and stuff i haven't got my period yet nd i kinda got not really just like really really small ones like im growing dem and yea like idk what to do i hate meat and i hate milk nd i don';t drink juice at all the only thing i like is pepsi and like junk food like hot cheetos...for lunch i eat hot cheetos and i get full quick idk what to do...can someone plz help me don't tell me to eat fast food thats bad for my health...