Suggest Treatment For Chronic Cough And Cold

Hi, I am Radhika Srinivasan. I have a query related to my kid's health. He is 3 years and 1 month old with a weight of 12.5 Kg. He was born on 13th of August 2008, normal delivery with 2.8 kg weight with good health condition. I have the history of asthama and hence he too is having the symptoms of Wheezing. For the past 3 months he is suffering from sever cold, and cough. Have taken all the test, primary complex chest x-ray, blood test, urinary test. But everything is normail, only he has chest cold. Have consulted many doctors they give only temporary treatment for cold. The cold is not reduced and he falls sick with fecer, cold and cough very often. I reside in Madurai, Tamil Nadu, India. Please suggest me what should i do to imporve my kid's heath.