Mysterious ailment affecting my 18 year old son

Patient: My 18 year old, 5 feet 6 inch height son who had been admitted to a fully residential college recently has come home for a month long holiday after a two and half month stay with the following symptoms: a) a persistent and frequent dry cough and b) a weight loss by an estimated minimum of 5 kgs! On being asked whether he has been a victim of ragging or abuse, he says no. The college hostel facilities are satisfactory and the results of his mid-semester exams have been good. He maintains a cheerful disposition and therefore I am absolutely dumb-founded in grasping what ails my son! A physician who was consulted today ignored his current weight of 51 kgs. and attributed his cough to a dust allergy, without any diagnostic tests though. The physician has prescribed inhalers like LEVOLIN, FORACORT, tablets like MONTEK LC, AZITHRAL and syrups like ASCORIL. My son and myself have reservations about his taking the inhalers and I wonder if the kind physician has really considered the case holistically. I request that I may kindly be given an advice in the matter, urgently, please. Many thanks.

Symptoms: Persistent cough and abnormal weight loss