My friend who does graphic design had the same thing for months... just constant aching that turned simple jobs into nightmares. She finally broke down and saw a doctor, who told her it was all about her setup and never taking breaks. Now she sets a timer to force herself to stretch every hour, and she got one of those goofy looking vertical mice. It took some getting used to but she says the difference is crazy.
That bit about the goofy looking vertical mouse got me. My uncle swore by his for years, said it saved his wrist from surgery. I tried one once and felt like I had to learn how to use a computer all over again. Could never stick with it long enough to get used to it, went back to my normal mouse after a week. I guess some people just get the hang of those weird ergonomic things.