Many computer users suffer from a malady called mouse shoulder. It is a repetitive stress injury caused by moving a standard computer mouse around on a desk. One remedy is to switch to a different type of pointing device, such as a trackball.
I've been using the Logitech M570 Wireless Trackball for a couple of years. I really like it. Today (1/20/14), Amazon is selling the M570 for only $27.50. If you are suffering from mouse shoulder and want to try an alternative pointing device without spending a lot of money, this is your chance.