skin on fingers

For the past few months, the skin on the thumb and index fingers of both hands has been drying and peeling, with painful cracking occurring. The skin keeps callousing and sloughing off. I have tried petroleum jelly, hand creams, shea butter and pure lanolin. I've seen a GP who suggested "contact dermatitis" and a dematologist and been given prescriptions for Protopic Ointment 0.1%, Dovonex 0.005%, Lac-Hydrin 12%, Fluocinonide Cream 0.05%, but nothing seems to help. There was no evidence of any fungus. This problem started with cracking fingertips last winter, which I attributed to dry weather and cold conditions - but it has continued for 10 months. The skin will dry and peel off, revealing new skin, which almost immediately begins to dry and callous. I am a very healthy individual, do not work with chemicals, wear rubber gloves when I have my hands in water for extended periods. I have taken a number of herbal and vitamin supplements for years, but have not started taking anything new which might be having an adverse effect. I suggested to the dematologist that they may want to do a blood test for strep or a virus, but was told this is just a form of severe dematitis. I was given the first cream treatment in July - nothing has made a significant improvement. When I start to use a cream, there will be a mild improvement, but then the problem seems to come back again. The skin on the fingertips will become so hard and dry that it literally splits open - very painful and aggravating. The only other place I noticed this was on my right big toe. What is going on here? Do I see yet another dematologist?