How To Treat Severe Cough,congestion And Shortness Of Breath In 3 Month Old?

Hi.My 3 months old baby is having severe cough and catarrh since 2 months. The cough is dry and the catarrh is thick and mucus-like. He can hardly breath with his nos. I have given him Flu-J and ampicilin, but the situation is still the same. What can I do?