9 year old chronic cough no other symptoms

Hi. My 9 year old son has been having a dry cough without any wheezing since the past 3 months now. He has been coughing non stop from morning to night but when he sleeps he does not cough in the night. He does complain of a slight chest pain and besides that there seem to be no other symptoms....I suspect the chest pain may be due to the incessant coughing
We have taken him to a few docters who have diagnosed him with mild asthma and he has been onto oral medications and inhaled dry powder(TURBUHALER) since the past few months but the cough only seems to get worse
Have done a food allergy test and have started the food elimination diet. Also trying to keep him away from the standard allergens like dust mite etc
What I immediately need to know is the following
What is the most probable cause of his coughing?
Is there any medication to give him a temporary relief from the coughing?(cough suppressants) as my heart goes out seeing him cough so much?
Do I need to do any more tests like CAT scan,allergy skin test, routine pulmonary test, methacoline broncial challenge test etc?
My next plan of action is to see both a Paediatrician who specialises in asthma and allergy and also to visit a Respiratory consultant who is a cough and chest specialist
Any response would be extremely welcome as I am very worried
Regards

[National Jewish]

Coughing that occurs so much during the day and goes away at night most of the time is not a major disease process.  Asthma, for instance, almost always gets worse at night.  Sinuses drain when you sleep and coughing usually wakes you up.  Lung infections get worse at night when you are lying down because the drainage accumulates.  Allergy to foods does not go away at night and dust mite exposure usually is worse when lying down in bed.  Seeing a respiratory consultant is a good idea.  That individual should be able to make the diagnosis and help your son.

[shastri20032003]

Thank you so much....will proceed with the pulmonary fuction tests
Regards