My son had a similar problem when he was the same age, and every time I would ask the doctor he would tell me things like you were saying. It never went away. When he was 2 or so he was sick all the time. Any and every cold, he got and it was all winter. I took him to a chiropractor (recommended not just picked out of a phone book or insurance book). He did knesiology and told me that it was asthma. He gave me a natural supplement for him to take and he took it for almost 2 years before he completely got better. Hope this helps.