Can A 9 Years Old Take Supplements And Protein Powder?

Is it safe to give supplements and protein powder to my 9 years old boy? He is underweight child his weight is 21 kg. He has been suffering chronicle problem since he was 5 months old. He have so many problems like his growth and development is very slow, he has no proper height, he has less immune system so he caught all infection quickly, he always face problems when weathers changed, If he try to eat proper food, the food not digest properly, he has weak digestion system. he has worm. I always de-warm him. If he eat saur or cold eatable, he face throat problems. He had take medicine for a long period like antibiotic, now these medicines are giving him problem like rashes on the body etc. please help me, what should I do for my lovely and only son.