Ergonomics man. You need to figure out what's causing it, aside from playing guitar, and try to correct the problem by doing the task in a different manner.
For example, if your pc keyboard is too far away from you and you have to stretch too far to reach it (or something like that). People don't realize how much a simple thing like typing can cause tendonitis.
^^^^^ VERY important stuff...
I have gone through this myself. Also to the point of selling & buying different guitars to find something that was less painfull to play & even considering accepting the fact that I might need to find something else to do all together. It's a horrible thing to go through if you truly love playing.
My main problem was actually the angle I would have my arm/wrist when using the mouse.....I'm a lefty that plays righty so my mouse hand was also my fretting hand. I say "was" because I now mouse righty most of the time.
I had what I would consider fairly major problems for quite awhile before figuring it out. Some days I was fine though...days I was away from the computer for extended periods of time though I did not notice the connection for YEARS. Eventually the problem got bad enough that I was in pain for hours after using the mouse for awhile nevermind playing guitar.
Finding out what was causing it... Look into things you do that are not guitar related.
When I realized the cause it still took a long time for me to accept it because the painful situations went away gradually. Then getting into a routine of a slow controlled warm up & cool down procedure has made a huge difference..
In short, the pain & discomfort I was experiencing that forced me to re-evaluate how much I wanted to play guitar has become almost non- existant... by changing the way I use my mouse!