I suggest asking your doctor to do an IgG panel including sub-classes.
You may have an underlying immunological imbalance that is contributing to the problem.
You could also ask for a referral to Infectious Disease for a consult or ask your doctor if he/she has consulted them already about
your bronchitis infection. If he/she hasn't then you may want to look for a new doctor as he/she probably should have done this back at abx number 3 or 4.
Other option would be a pulmonologist who treats airway diseases. They may have some tricks to help.