Chronic Day Time Cough

[careers4u100]

My son is 11 years old .Since three months he is coughing persistently ONLY in day time and during night while sleeping he doesnot cough . I took him to the regular doctor ( Pulmonologist) who treated my son for allergy and childhood asthma since 2009.The doctor took an X Ray of Chest PA view .He said the X Ray was clear .As usual prescribed Methyl Prednisolone for 5 days , Budecort and Levolin Rotocaps and Montekulast .The cough didnt go and after a week ,revisited the doctor . He gave a dose of Azithromycin for 5 days . Even later to it it didnot go . .Currently my son is consuming Budecort , Levolin and Montekulast and the cough doesnot go .OTC medicines diphenhydramine,Codeine (10 mg) + Chlorpheniramine (4 mg) didnot work either . There is no cough while he sleeps . Any advise please ?