I have just two thoughts
Keep in mind I've not used a wireless mouse... but... my first thought is to suspect a driver conflict of some type. Have you installed or downloaded anything new proximate to the time you started having the problems? The other thought is whether there's any way its (infra red or whichever, the place it transmits from to the computer) port has become dirty, also, perhaps a little piece of something has gotten under the button, wheel, etc.?
I am slowly falling apart - I wish you'd take a walk in my shoes for a start. You might think it's easy being me ... Sometimes I find myself shaking - In the middle of the night. And then it hits me and I can't - Even believe this is my life
(The Wreckers; "Stand Still; Look Pretty")