My baby still has symptoms.?

My baby is now 4 months and 2 1/2 weeks old. He has had cold like symptoms since he was 3 weeks old. It started out as congestion, then his eyes water, next he had a cough. About 3 weeks ago he got really sick and was on antibiotics. After he got over the chest infection he still has the congestion and coughs worst now. He also has a soft airway. I keep taking him to his pediatritian and now he said that all he hears is a cold and gave him c-phen. he had c-phen before he got really sick. His congestion isnt getting any better if any thing its getting worst. What should i do!? I want to change my doctor but dont know if i should do that either. He wont do a chest x-ray and he said he cant tell if my baby has allergies. It makes me so mad. My baby's cough wakes him up and some times he is so congested that it sounds like he cant breathe then he coughs for minute on end. Can any one tell me what this. The doctor doesnt think he should go to a specialis either. I use baby vapor rub and it doesnt seem to help.