Maybe it may be because you aren't used to cold weather and your finger is reacting to it
or strained a muscle or tendon somehow? lifting, etc..
to put it in a medically scientific way:
put your hand on your other shoulder, and move that arms middle finger, you can feel movement in the area up there.
were you working outside in that cold, or something injured that fingers nerve?
I pinched my finger once and it took about a month for the nerve to heal, wasn't painful, just couldn't feel anything.