I have some sores on my back and on my arms but wont heal, although a scab forms. the scab is yellowish and reappears really quick if it comes. ?

Arm sores: There are certain limitations imposed by this format which include the lack of a photograph of the skin lesions about which you requested information, So it's impossible to tell you the correct diagnosis and/or therapy, My Best advice would be to call and make an appointment with the dermatologist. There are many conditions which make chores only arms and these definitely need to be looked at.