Well it's clear you're depressed. Now, from the brief information you've given, i can't really pin-point the root of the problem, however, if your friends are putting you down all the time, they clearly aren't your friends at all. As for the cutting, i suggest you go and see your doctor. He/She'll be able to transfer you into the care of a community mental health nurse. Ok, that sounds scary i know, but really it isn't. The mental health nurses i know are lovely people, and so down to earth, you cantalk to them about anything. Once they've had a few sessions with you, and you feel a bond of trust between the two of you, the mental health nurse will identify what your problems are then recommend various other professionals who can help you.
I hope it gets better for you soon hun *hugs* xxx