Our society with it's "work out, get fit" mentality has preached the mantra "no pain, no gain" for so long it's easy to think that tendonitis is something you can just play through.
That is definitely not the case!
I developed carpal tunnel/tendonitis from computer usage 11 1/2 years ago...it didn't occur until we moved to windows-based software - the mouse-clicking did me in. It finally got so bad that I had to stop playing guitar, golf, and a bunch of other stuff.
It's been a long process getting better...I still feel it if I overwork on the computer. Fortunately, once again I can play guitar as much as I want.
Things that help:
1. Ice. Tendonitis is an inflammation of the tendons, and ice works fast and effectively. I used to ice my wrists after playing guitar (I've now gotten to the point I don't have to)
2. Stretching. A physical therapist showd me how to stretch my rib cage area (the thorasic region, to you medical types) to overcome the affects of bad posture. This allowed for better circulation down my arms.
3. Muscle tone. The year and a half that I stopped playing guitar, my left wrist, (which wasn't as bad as my right wrist) continued to plague me. When my right wrist got good enough to play again, the problems in my left wrist went away...apparently from redeveloping the muscle tone.
And, the hard one:
4. Time.
Being debilitated by a computer injury definitely makes you feel like a wuss, but suck up you pride and treat it like an injury, and you'll put it behind you.
JR