Need Pulmonologist. He gets better soon?

Hi, my 2.5 years old sun weight 11.7 kg is suffering from cough from past 11 weeks. the cough reduces sometimes and we think that it is going to be better ,also doctor(MBBS DCH) thinks the same. But the cough increases again in some days and not going away completely. He is taking multivitamin A and d3 Syrup from past 3 weeks, also had some medications. Last week he vomited after having milk but just before that he ate few grapes so we thought it was becouse of grapes. today again he vomited with coughing after having milk and daliya. What should i do so that cough does not increases and he gets better soon ? He is going to school and doing daily activities without any problem. I have heard that pulmonologists know the respiratory system better than child specialist.