http://en.wikipedia.org/wiki/Dermatillomania

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Dermatillomania (also known as compulsive skin picking or CSP) is an impulse control disorder characterized by the repeated urge to pick at one's own skin, often to the extent that damage is caused.

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This sounds quite similar to what you've described, so I just wanted to let you know that it is something recognised by the medical profession, and something you can get help for, y'know? You mentioned that you do it when you're nervous, which wikipedia and other sources tell me is quite common. I think it's great that you're trying to control these urges, but I really honestly think it would benefit you to try and seek some professional help with this. Help to control your nervousness and anxiety - if you learn how to do this, then perhaps you won't feel the need to pick at your skin so much, hmm? I also found this on the net, which might help a bit:

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Cognitive Behavioural Therapy (CBT) and/or Anti-Obsessional Medication are the primary treatments for CSP.  If CBT is unsuccessful you may be referred for Habit Reversal Therapy.

Helpful hints on breaking the habit of skin-picking:

• Get advice on skin care. If you have a skin complaint see a dermatologist.
  
• When tempted to pick, care for your skin by applying a moisturising lotion instead
  
• Stimulus control: cover or remove mirrors if they act as a trigger and get rid of all implements such as tweezers and pins used for picking.
  
• Consider the use of artificial nails to make picking more difficult � it may work for some.
  
• Wear rubber fingertips or cotton gloves whenever possible if you feel the urge to pick.
  
• Try replacing some of the sensory aspects of skin-picking with a more desirable alternative. For example, keep an object by you that you can manipulate (squeeze or pull) such as a soft rubber ball or some Blu Tak.
  
• Keep your hands busy with something else such as a puzzle or knitting.
  
• If you bite the inside of your cheeks try eating crunchy snacks when you feel the urge to bite.
  
• Reward yourself for making progress with some kind of treat.
  
• As you gain more confidence gradually begin to expose your hands, arms, face or legs to others starting with family and friends. You will no doubt benefit from their support but at the same time the negative consequences of engaging in your habit will be increased.

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Taken from here: http://www.ocdaction.org.uk/ocdaction/index.asp?id=348

I do wish I could help you more, but as I said, I do think you should seek medical help for this. It really can't be good for you, obviously, so the sooner you receive help for it, well, the better.

Take care.

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someone tell me i'm dreaming,
the freaks are rising up through the floor