tendonitis? Lack of sleep? Dehydration? Lack of potassium? Inadequate diet? Lack of exercise? Repetitive movement? Crappy posture? Who knows! Have you have already addressed these issues bt the problem interferes with your quality of life then go see a doctor. If you aren't sure what it is, go see a doctor to get some peace of mind. Do you really want to be saying to yourself, "if only I had seen a doctor earlier"?
Personally, I would rather be able to say, "Well, don't have to worry about that anymore."
Hope you're ok.