I would definatly reccomend a specialist if you have concerns about him, I would say get any and every opinion you can get, keep us posted on how he is doing .
My daughter was 7 weeks early. Since she was a premature the Dr.s made it mandatory she get RSV shots. This helps the child from getting ill, It sound like if your child did not get these shots he might be getting symptoms of RSV. Here are some I know of: having a simple clear runny nose and occasional cough that can be treated at home, to severe difficulty breathing that may require hospitalization. Other symptoms might include a low-grade fever, sore throat, headache, and irritability. Younger children, especially those under 2 or 3 years old, are most at risk for more severe symptoms, such as high fever, wheezing, difficulty breathing, a persistent cough, or apnea.
I hope this helps.