Hello I just want to ask what is the best medicine...

what is the possible causes of your medical condition ?
autoimmune diesease such as eczema arent caused by clear cause , but its believed that there is some factors like :
1. family history 
2. existance other types of sensitivty disease 
3. stress 
4. enviromental factors 
What to do next ?
- for now , use a topical steroid medication such as delor ( contianing higher levels of cortisone ) 3 times a day 
- follow those advices :
1. Use relatively warm water for showering ( not hot water )
2. Avoid expose your son to the sun and heat sources
3. Avoid environmental stimuli for eczema, such as atmospheric or skin contact with a specific thing or food
4. Avoid using any product that has aromatic or irritating ingredients to the skin
2. avoid any possible caused of your allergic reaction 
if the symptoms didnt get better or lasted longer than expected , what to do :
consult a dermatology doctor as soon as possible 
 doctor will perform some tests to determine the treatment pathway such as :
- clinical examinations 
- effected area culture test
- IGE blood level test - ( the normal range is : 0 - 300 ) 
the treatment option in the case is : steroids ( IV injection and daily oral )