Could be a chronic fungal sinus infection. Most chronic sinus issues are fungal (per research done by an ENT at Mayo Clinic).
Post-nasal drip may go into your airway, irritating and inflaming it and causing difficulty breathing, especially if the drip contains fungus...
Have you tried a saline nasal wash?
Chronic Lyme, Bart., Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut dysmotility & non-specific inflammation, Lupus, Osteoporosis, etc.; G-Tube; TPN-dependent
Meds: Flagyl, Zofran, Acupuncture, etc.