As a heavy computer user, I used to have a lot of problems with my right wrist. I thought I was getting a serious case of carpal tunnel syndrome. I often had to massage my wrist, and I also used some interesting stretching techniques to help relieve the discomfort. I'd heard of people who needed surgery to correct the problem, and I thought that would eventually be my fate.
Then I realized there was something I could do about it. I've figured out a few things that have changed my life, and I have no discomfort any more. Most of my problems come from the mouse, and I really believe that's where most other people's problems also lie.
Here are the things I've learned, and suggestions to help you with this type of problem:
I know what you're thinking: "I'm right handed, I could never use the mouse on my left!". I'm going to appeal to bravado here and tell you to get over it. Don't be such a baby. Humans are the most adaptable animals on the planet. It's the reason we have houses, cars, running water, and computers. It'll probably take you a day or two, maybe a week to get used to it, but the alternative is pain and eventually surgery... surgery that might not even work.
I know people who have taken this advice, and have never looked back. This is one of the biggest changes you can make, and you will probably start to have results in about 2 weeks. Here are a few tips on adapting to using the left side:
Most of the (optical) mice I have seen are too heavy for their size. One day, I took out my screwdriver and opened one up to find out why. What did I find? A big chunk of useless metal bolted inside!
I'm not sure if this is to prevent the mouse from feeling like a cheap piece of plastic, or if it has something to do with precision, but I removed it. Ever since, I have not noticed any difference in how the mouse works. All I know is that it's much lighter, and the muscles in my hand stopped bothering me. All you need is a Phillips head screwdriver.
Lighter = Easier to Move = Less Strain on Your Hand
Eliminating this problem is pretty simple: Don't rest your arm on the edge of the desk. Sometimes awareness of what you're doing is all you need.
So there you have it. It's not profound, but I hope it helps you if you are in discomfort, and maybe gets you thinking a little more about your own ergonomic setup. Ergonomics is about what makes you the most comfortable, and each person is different. If you are having problems, try something else! You'll be glad you did.