Sounds a lot like what I had a few years ago which turned out to be from spending hours at the computer with my left forearm resting awkwardly against the edge of my desk. Was alarmed at first, but then realized that laying off the computer for a while sorted things out very quickly. Longer term it's all about ergonomics -- raise chair and/or armrest, lower keyboard ... That was it. 'Course, I'm no doctor but if it is what I think it is it should get better quickly, no doctors necessary. Otherwise it's more likely to be carpal tunnel or something similar. No harm trying, right?