You may have bronchitis but it may not necessarily be infectious, viral or bacterial. You could be having acid reflux with recurrent aspiration or some type of swallowing disorder with the same outcome. This is not lactose sensitivity. You definitely should have your upper intestinal tract checked out by a gastroenterologist, also known as a GI specialist.
Or, the problem could be infectious but with organisms that can cause chronic/recurrent lung symptoms of bronchitis. Specifically this would be an atypical form of tuberculosis (TB) called nontuberculous mycobacterium (NTM) such as mycobacterium avium complex (MAC). You should see a lung specialist and should definitely have another chest x-ray and may need a CT scan of your lungs.
Finally, you will want your doctors to make sure that you are not suffering from chronic sinusitis, in particular allergic fungal sinusitis, a condition that can cause all the symptoms you describe.
You should discuss this information with your doctor.