Any updates? We are in similar situation?
My son is 4 yrs. old with the same wet cough, it's a non productive cough that comes and goes. It flares up when it's cold, or smokey, or when he's active. It's asthma, he has had problems for the past year with it. It started out when he was sick, he was wheezing. It got so bad they put him on prenisone. The next virus, the same thing happened, then they put him on Singulair hoping to keep the wheezing at bay and keep him off of the dangerous prednisone. Well, now every time he gets sick, the wheezing flares up and he has a nebulizer we use to keep it under control. The past few months of sicknesses has been the worst. He was on prednisone 3 more times and still while on Singulair. Now he is on Flovent and Singulair hoping to keep his wheezing under control. But he remains with this wet cough. It's from the asthma.
Has your son ever had wheezing? The Singulair is pretty safe although it can have sleeping side effects. We have to give to him at night right b-4 bed or it keeps him up. It has helped, but just not enough. I've been told that boys seem to outgrow it more than girls and we are hoping for that. It's hard to diagnose asthma in kids younger than 6-8 yrs. old. But I would try and keep him off all drugs as long as possible until you feel he really needs them. After awhile they lose their effect and if it was to get worse then they wouldn't be as effective. Go with your gut, mother's do know best and doctors just do their best guessing.