I Have Been Feeling Very Depressed Epically During The Hours

I have been feeling very depressed epically during the hours of the night and i have been starting arguments with people lik close friends and family for no apparent reason and I've been very irritable the past 2 weeks and I don't understand why I'm usually a very happy birthday at school I'm 15 people even say sometimes I'm to happy and I talk fast but inside I'm actually dying inside wanting ti ask my friends for help but i dont want to bother them with my problems and when I ask some friends for help they always say why are you acting depressed all of a sudden and its no just all of a sudden its just sometimes im happy and sometimes im sad but idk whats wrong with me i just knkw that I'm both happy and sad and I'm still trying to figure out how that can be someone please help me and tell me whats wrong with me and tell me how to turn off my bad thoughts so i can be only happy its ruining my friendships with people i love