I don't think I have an answer, just encouragement to yes, go see the specialist. I got bronchitis as a young adult when I moved to a very dry cold snowy city in January from a humid climate (MD) and then when I moved on to San Diego in May, phew, I had problems!! I got sinus problems for the first time and ever since then when I get a cold, it then goes to my lungs (not 100% pf the time, but much oftener than I'd like!).
I truly believe that once you've had bronchitis, it sets the stage for other respiratory problems ie, pneumonia, sinusitis, maybe even allergies, and so on.
2 years ago at this time of the year I was dx'ed with bronchitis/walking pneumonia because I'd gotten sick right at the end of the semester with the stress of creating, giving, and grading final exams to a roomful of college students and of course Christmas preparations and all that at that time of the year. Anyway that went to my lung and I did have an x-ray to show that it cleared up, but I STILL feel a pain in the back bottom of my lung whenever I take a deep breath. I hate it. It does seem to ever so slowly be getting better but I still hate it.
Does your son have allergies? Sinus or post-nasal drip? Those might be contributing.