Kindly have your hand examined by a doctor to rule out carpal tunnel syndrome, as it seems to fit your description, which could be treated relatively easy. As CP3kids suggested, a neurological examination is required.
Have you ever had a lab test called ESR or RA panel done? Both tests are done with blood work, and can help to rule out rheumatoid arthritis. Have you been spending lots of time on a computer, word processor, or keyboard lately? If so, you may have some carpal tunnel symptoms going on, that typically presents with the thumb, index and middle finger symptoms. At any rate, it would probably be a great idea to go to your primary care physician and get evaluated for this problem. He/she will be able to some DTR's on that extremity to check for nerve related issues. Good luck to you!