How did everything become like this?

I changed from an happy little girl to a depressed teenager even tho I never had any traumatising moments stil im completly different then before and im insecure i hate my body and everything about my self.My life is not bad i have everything I need and other people have it worse than but i still hate it here i hate this world its not fair how many people have nothing and other people have to do nothing and still get everything i just dont understand how the world can be this cruel? I mean isnt there suposed to be a god or smth (i dont know what you belive in) that is suposed to be helping people ? I just dont understand and i dont wannado it anymore i dont wanna be here anymore its just so exhausting.