Again

I did it again. I just can't seem to stop, my penknife is right by my bed so i guess it doesn't help. But every time I hide it and forget about it, I go find it when I feel depressed. Pain is the only feeling I can actually feel properly, and it is so addictive I can't help it.
I wonder why people don't notice, but then I remember they just don't care. My friends just don't notice that I have changed, I mean drastically changed.
I don't know what to do, I can't just stop. I can't feel nothing, it's like I'm nothing, a void, that can't ever be full.
The reason i'm writing this is because I overheard someone say writing things down helps. If anyone can help, please do.