Hand pain from using the mouse too much

It does sound much more like an ergonomics issue than a mouse issue, as I've had similar problems when I was stuck at uncomfortable desks and workstations. In addition to what Soulzar said, when you move your mouse around you shouldn't ever have to actually pull the cable. I've found a lot of people leave the cord of the mouse hanging over the back of their desk and it gets caught up in a bunch of other cables, requiring you to use a lot of extra force to pull the mouse towards yourself which can cause wrist strain very quickly. Either untangle the cords, find a different way to set it up, or, my most common solution, pull as much extra cord as you can and scotch tape the mouse cord at the back of your desk so you have plenty of slack while you're mousing.

Jam it back in, in the dark.

gaming, I got two of these: Amazon.com: Gripmaster Hand Exerciser Red, Medium Tension (7-Pounds per Finger): Sports & Outdoors (one with medium, one with heavy tension) to help with my golf grip and finger fatigue from writing/typing for extended periods of time, and I've found as long as I'm active in using them, they help me out. If I quit using them for more than a week or so, I go back to being pretty much how I was before starting the exercises.

Where exactly is the pain in your hand? Generally when I've had ergonomic issues with my mouse/keyboard it's been more in the wrist that can flare up through my fingertips than "in my hand."

How ya doing, buddy?