Suggest Remedy To Prevent Recurrent Cold,cough And Wheezing

Hi,My son is 3 years old. He has a history of on and off cough since he was 9 months old. It starts with runny nose followed by brassy cough n slight itching in the nose and it worsens to wheezing.His weight is 16 kgs and height is 101cm. He was prescribed the following:1) Syrup Cetzine 5 ml at bedtime for 5 days 2) Asthalin MD 1, 2-4 puffs, every 4-6 hours with spacer for 5 days 3) Start Montair mg at bedtime for 3-6 months The doctor gave him 2 puffs of Asthalin with spacer at clinic n later i didnt as his cough vanished after a single dose of Cetzine. I didnt even start Montair fearing too much medication going inside him.On 21st August 2013 he again got bad cough, wheezing and breathlessness after he had a small tetra pack of cold litchi juice. He was prescribed Bricanyl, Omnacortil 5mg, Cetzine, Singular and Nebulization. He was fine after this but yesterday he again had two licks of melting ice cream n today 2 slices of cucumber with a dash of lemon. This has worsened his cough, there is no wheezing yet. I gave him 2 puffs of Asthalin twice today n now 3ml Cetzine. From 21 august till date i have given him Omnacortil 4-5 times; i.e., 4-5 bottles of 5mg. Now docs say that so much of Omnacortil is bad n has changed the prescription which is as follows Budecort 200 inhaler 2 puffs morning n evening for 6 months Asthalin inhaler sos Nasonex when cold starts How do I increase his immunity and prevent this recurrent cold, cough and wheezing? I dont want him to get used to Asthalin puffs n Montair will have Liver enlarging side effects, so I want to avoid that too. Please advise.