If you do something repeatedly, or have a habit of using your pinkie for typing alot, you could be developing minor carpal tunnel, thats what I suppose.
Although, pain in the side of the hand could be a sign of arthritis, depending on your age. Get a checkup, and if its just a cramp you can hope for the best.
EDIT: Read hill's last post, your most likely developing Carpal Tunnel, you might wanna see a doctor.