What is wrong with me?

I am sad all the time. I dont like to do anything i used to do... or anything at all i dont even want to skateboard and a few months ago it was all i ever did and i am allways turning down invitations to hang out with my friends cause im never it the mood to hang out. I am having to force myself to eat cause im never wanting any food and when i do eat i get even more depressed. I am allways puting myself down i cant think of any good things about myself (probably cause there is nothing). I allways feel like life is pointless and most of the time i just wish i was dead. I cant pay attention in school and i fail a cl for the first time. please i really want to know why im feeling like this.