There are many reasons to have congestion in children the age of your son. I suggest that you work on this problem with your general pediatrician
, who knows your child's health best.
There are many reasons to have chest congestion. First of all, it could just be that your son has had a run of colds. Quite frequently, just by chance, these can affect a child and give the impression that they have a weak immune system when, in fact, it has just been bad luck.
It is also possible that your son is developing symptoms of asthma
or that he has allergies that are provoking a chronic cough and congestion.
is a cause of lung symptoms. However, people who have cystic fibrosis suffer from repeated pneumonias and other infections. Congestion alone, in the absence of infection, would not be itself a sign of cystic fibrosis. Of course, if your son does develop several lung infections in a row, then a standard part of figuring out why would be to test him for cystic fibrosis.
Start by talking with your pediatrician - they can help you figure out whether additional workup is needed or if a particular treatment should be started.