Some factors could be that you become too nervous, if its not being nervous, it could also be because you're stressed, like you said, taking notes, you may strain your fingers, write too hard, hold the pen too hard or something similar.
just try to be really relaxed, deep breaths, good posture helps
Im almost postive this is a medical condition and you should definitely see your doctor. Otherwise I think they sell a body wash that can help with body sweat.