I agree with others... don't ignore the pain...

Seems odd to me that you only have pain when mousing and not just general computer work. Maybe it's the angle of your wrist when using the mouse. Perhaps you might consider trying an alternative mousing device, ie. vertical mouse, scroll bar device, touch pad, etc. The have alot more options now for pointing devices.

You might also consider standing (rather than sitting) at the computer. I switched to a sit-to-stand desk so that I can stand and do computer work. It helps. I don't slouch as much when standing.
good luck with it...