I also started self harming when I was 15 and thankfully seem to have stopped, I had CBT but I don't think it actually made much difference.
For me it is distractions that work. I still get the urge to self harm very often but I have developed healthy coping stragies to stop me.
Similar to what Suzie said about getting a punch bad (which was brill advice!) think about what makes you feel good. Sit down and make a list of all the things that make you feel good. Take out self harming ones, cutting, burning, bruising in your case or anything similar like over eating or drinking too much alcohol.
What you're left with are your distractions. My main ones are exercise, music and writing.
So whenever I get the urge to SH I go for a jog, listne to some music or do some writing. Writing can be good especially because it could even be just writing down thoughts and feeling which sometimes makes you realise thoughts you didn't know you had until you write them down.
To put it briefly, think about what makes you feel good and is safe, and when you want to self harm do those things instead.
I'm not surprised it's taken you months to write this question because you're right, it is a very tough thing to talk about but the fact that you managed to write the question and have acknowledged that it's a problem is half the battle. Tamborine is right, it's usually something you can't fully tackle on your own. Even if you've tried counselling and CBT before it might be a good idea to give it another go or ask your GP about what other things are available to you.