Why bother with the number pad? Teach yourself to use the top row of the keyboard, using both hands. That way, neither gets overused (and you just go down with RSI in both arms at once...)

Muscular pains are often all lumped under "fibrositis" or "fibromyalgia" which gives it a name but doesn't cure it. There are many possible causes, and it's not helped by the fact that the cause might not be in the area that hurts. Chiropractors are specialists in tracking down pains in your back to the type of shoes you wear, or aching feet to the wrong kind of toothbrush. I think a massage by a bronzed 22 year old man with a sixpack might help.