Depending on which finger it is, it can be carpel tunnel syndrome, compression of
ulnar nerve, compression of radial
nerve. Diabetes or hypothyroidism too can be the cause. Very cold climate, peripheral vascular disease, panic disorder, leprosy, alcoholic neuropathy, compression of cervical spinal nerves, are the other causes. It is difficult to comment beyond this on net without examining you and a detailed history. Please consult your PCP to begin with and get a referral for a neurologist.