ENT problem to my son. His immunity!

Respected Dr. Sahab Good afternoon. My son is 11 years old. He is suffering from cold, cough and tonsils from the age of 4 years i.e. from 7 years back. He remains affected by it after every fortnight in winter season and rainy season. Even after staying at home, he is affected. We are getting his treatment from ENT aliphatic doctor. During treatment and one week of post treatment he remains ok. Then again caught by the same problem. His immunity is also weak. I have some doubts in my mind. Upto the age of 4 years we was ok. His health and diet was good . Then he was given  vaccination of Rota virous. After that I feel this problem occurred. Kindly clear my doubt. And suggest me the way to overcome this problem permanently and enhance his immunity