Hi, my son is 3 years old, he has been coughing for 5 months especially during the night and soon he wakes up. I took to many doctors, his chest is clear but he has a blocked nose and i have a feeling that his nose condition is causing the cough. he eats well, plays well and he looks ok but this cough is not going away, and gets worse when there is a change in weather. what to do?