I tried the elastic band thing once, and my GP told me to stop it because it was annoying!! Didn't mean to be annoying, but doctors and just the surgery itself make me very anxious.
I have to say, although I wouldn't encourage anyone to self harm, at times it is the lesser of two evils. Is there anyone you can talk to about it? A good friend, family member or someone? I know how hard it can be, but there are times where I just need to vent my anger/frustration or whatever it is and that can at times do the trick. Sometimes nothing does and I give in. It's not an easy thing to avoid if that's what you use to cope