Sounds like a case of bad circulation to me. I'd get up and walk around for a couple of minutes to get the blood flowing, maybe do some stretches or something.
Also maybe check the position of your hands and arms to make sure you're not cutting off any blood flow.
Seeing as your hands move when you type, you shouldn't really be getting cold fingers, because that movement increases blood flow the area.
I'd probably see a doctor to be quite honest. Or you could just buy a macbook and put your hands under it for a few seconds, that should warm them right up