I'm sorry you are having such a difficult time with this. But I do know something about it. In my case I finally stopped once I had done irreparable damage to myself. And even now I still feel the urge.

Here are links to 2 articles, from PC's archives, that (hopefully) may offer some useful suggestions. The second article is aimed at parents of children who self-harm; but I think it still offers some potentially useful suggestions for anyone:

How I Stopped Self-Harming

Helping Your Child Reduce Self-Harming Behavior

My best wishes to you...