I had similar problems and switched hands, and most importantly, use a trackball. For me, the act of gripping the mouse seriously exacerbated the problem.
How long did the pain go away in your primary mousing hand after switching to the other?
I did that in combination with getting a Kinesis, and over the period of a couple of months all the symptoms were gone. It was bad enough before that at the peak that I couldn't button the small buttons on my shirts.