It is very difficult to be sure what is happening here without being able to examine your son. This is obviously not just the flu as he would be better by now. He appears to be losing weight and is ill and is pale. There could be many reasons for this particularly illnesses such as glandular fever or TB. He needs to be seen by a paediatrician who will make a proper diagnosis. I see that you have already taken him to 3 doctors, but you really need someone who is going to find out what is wrong with your son. If you write in again and tell me in which city you live I will recommend someone.
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