What's your pediatrician is saying for your child's illness. Have you done any investigation for your child till date.I will recommend certain investigation for your child. CBC,
CRP, ESR,
LFT,RFT, urine culture and sensitivity. X Ray chest, Mantoux test on left forearm for TB. Widal test for typhoid. USG abdomen. IgE level for allergy testing.
After that your pediatrician can decide further course of your child.