Hi, My 3yr Old Son Caught Cold And Next Day

hi, my 3yr old son caught cold and next day i observed phlegm in lungs . same day evening for the first time he started breathing like asthmatic patients. we used nebuliser. It gave some relief. we waited for 5 days and followed home remedies. there is very mild cough but i could hear the sound that there is lot of phlegm inside. Two days back we went to a doctor, he prescribed brezvent ,Augpen and kidpred. Till today there is no much change. What shall I do.