Why am I such a failure in life?

When I try my hardest, I fail. Ever since I've started my GCSE's, I've fallen into depression. I'm falling behind in cles, I try hard concentrating but still- nothing. I've always hated myself for this. I want to make my Parents proud, I want to make my family proud, I want to make my teachers proud. I want to prove everyone wrong and show them that I am not a failure. Clearly I am. Even my friends say so. I seem like a jolly and bubbly person on the outside, but inside... I'm just a depressed little sh**, who's failing her life. I can see my future- A dustbin cleaner, better yet.. A fat couch potato, munching on packets of crisps, eyes glued to the TV, with her belly hanging over her t-shirt. Great. How can I stop myself from being such a failure in life? :|