The NUMBER ONE thing you should do is CONSULT A DOCTOR.
Doing hand stretches, exercises, lifting weights, icing, or heating, anything like that can do more damage than good if you don't know what the problem is and why it's happening. Many conditions become worse with over stretching and with weight lifting, please, please avoid this stuff unless you know what the problem is.
Simply resting until your hand feels better is really the only advice I think is worth listening to until you know if you have an underlying condition or not.
That said, I do think re-organizing your work place is sound advice. I've found that lowering my chair so that my arms are more at a 90 degree angle with my desk helps a lot, adjusting pen sensitivity helps, and more importantly, try drawing more with your arm/shoulder than with your wrist (this should help make your strokes more confident as well, it's a tip I've gotten from many life drawing teachers) Plus, keep in mind a small tablet will often cause hand/finger pain with lots of use because your arm/hand can't move around as much, but I don't know if that's something you're dealing with.
But again, please don't do anything serious until you SPEAK WITH A DOCTOR FIRST, I CANNOT STRESS THIS ENOUGH.
Good luck!