Had the self same problem. Was referred to a physio and was diagnosed as the first symptoms of RSI. She told me to get a track ball mouse. There are various sorts but the one I chose (and solved the problem) has the ball in the centre and the traditional left and right clicks are to each side. The mouse stays still, you move the cursor by swivelling the ball with your first two fingers and left click with your thumb, right click with your third or fourth finger. It spreads the load and limits small repetitions. Only get the pain if I revert back to a normal mouse now. You may find you also have the other symptom I got which was pain in the upper arm as if you'd been punched and got a "dead arm" like in the old schooldays. Good luck, don't ignore it.