Itching and some marks. What he used to.

Hi my son who is 3.5 years old has got skin problem on his whole body and that continuous for the whole year his doctor said that he has got dry skin and asked to apply moisturiser lotion but even then he was to scratch the areas and gets a dark mark there iam really worried for him some times his whole body gets that and when he itches blood comes out. Please suggest me what should I do. When he was born I was using teddybar soap for 2 years and once changed to Himalaya bar and as he got this problem I stoped using that soap and dint apply any soap on his body and then when got appointment with his doctor he suggested cetafil product of which iam using bar and moisturiser lotion now but even he has got the same problem. Please do help me because I can't take this any more.when ever he itches I really feel pain what he used to.