Six years of throat irritation with a clean HRCT, no fever and stable weight tells me this is not a lung problem at all. What you describe - thick morning sputum, choking spells, worse in humid or dusty air, better on some days - is classic silent acid reflux irritating the voice box along with an allergic drip from the nose. Steam and gargles help only briefly because the acid and the allergy keep restarting it. Treated properly for a few weeks, most patients get real relief.
Next Steps
Take an empty-stomach acid blocker daily for 8 weeks, add a night-time antihistamine and daily saline nasal rinse, avoid late dinners, tea on empty stomach and smoking or dust exposure. Get spirometry and a simple ENT scope of the throat if the choking spells continue. You can consult me on Practo with the HRCT and I will write out a stepwise plan and review you at 4 weeks.