What Causes Dark And Thick Skin Around The Knuckles?

Hi, I am 17 yr old . Its been years I have strange skin around my nuckles , the skin is dark , thick , old looking . I went to many doctors . But all the do is gives medicine and ointments. I always timely had my medicine , but no difference. Recently my dermatologist gave me a ointment that was to be applied on the skin where the black covering are. First two days the ointment worked and my skin was comming out and I was able to see my actual skin. But then my skin became red and then back to the same skin I had before . Now the ointment dont even seems to work. When ever I sweat the skin becomes bubbly and white . Even if I keep my hands in water for 10 mins . It feels embarrassing. I now have no hope but plz help. Thank you