Your description suggest that your son is suffering from allergy and may even be having asthma. It is better to subject him to some tests to establish the diagnosis. These tests are CBC, AEC, X Ray chest and a PFT. This will help in ruling out any infection and diagnose asthma. In the meanwhile give him inhalers like seroflo, a monteleukast and an anti allergen beside a short course of steroids which he is already taking.