When I need to edit severely a long piece of writing for work, my wrists are usually fine -- but my index finder tends to stiffen and get a bit sore from manipulating the mouse o'ermuch.
What mouse pointer are you using? I use a Logitech MX500 and never had that problem, mostly because the design of the MX500 makes it very comfortable to use over long periods.
A cheap, possibly free solution would be to look at your mouse driver and see if it allows you to switch the left button with the right and try that. Assuming you're not on a mac. or using a one button mouse, of course.