Hi, welcome to HCM.
From your history it appears to be starting of Atopic Dermatitis
in your son. It is a simple eczema
of infants and children manifesting any time within 2 to 6 months of infancy.
The Medications you are using is correct (hydrocortisone cream
, and Oilatum), with this you should use an antihistaminic drops ( syrup) round the clock to minimize the itching. you should not use diprobase
as is definitely bit strong to be used in infants.
Along with this you must keep the baby in soothing environment with simple cotton clothes and not any synthetic or fancy clothes ( mother also should wear cotton clothes as the baby is continuously with mother). Prevent mosquito bites, cover the hands with cotton gloves so that kid is not able to scratch him. With this you should also trim the nails ( Carefully!!).
You give Luke warm water compresses on the affected area which will soothen the skin.
You should meet a dermatologist
to solve out the problem.
Hope this information will help you.
Dr Sanjay K Kanodia