Dry cough for more than a month

Dear Experts,

My son is 3.5years old. He suffering from dry cough from more than a month now.
Currently he is been advised asthalin expectorant and allegra 30mg /5ml and seroflo 50MG twice a day
But there is no improvement in his cough. He doesn't cough continuously, but when the cough starts he coughs at least 10 to 15 times continously and at the end it seems like he will omit but doesn't omit always.
He weighs 13.7KG. He eats properly sleeps properly but the cough doesn't seem to cure at all.
I am really worried. Please suggest.

[margypops]

I am wondering if this could be allergy relatedwhen he has a  spasm of coughing what had he been doing, eating, drinking , anything happening prior to it, is his breathing okay no asthma ? any fever , sore throat,certainly if its continuing take him back to the Doctor .Good luck