"To be nobody-but-myself in a world which is doing its best, night and day, to make me everybody else means to fight the hardest battle which any human being can fight, and never stop fighting"
Although very technical at times, this article is very valuable in describing the different mood disorders and other conditions that lead to Self-injury.
Sometimes fairly technical, however this article discusses many different possible causes for the incidence of Self-injury
Though not all specific to self-injury, there is a plethora of good information here, so check some of them out and maybe you will find just the help you are looking for!
Copied with permission from the excellent website devoted to self injury, "Secret Shame" found at: http://www.palace.net/~llama/psych/fself.html