Good to check with another doctor. Lung function decrease is most worrisome. I had to go on Oxygen 10 years ago with the Non Tubercular Mycobacterium. It required Infectious disease doctor and what we call the "Big 3" antibiotics. They worked, but my lungs filled with Candida. I used Candida cleanse to eliminate it and as per bronchoscopies, that worked, too. I have been exacerbation free for 10 years. Only on oxygen for a year while we figured things out.
A good practice is to take your medical history with you to every appointment. Your description for this group was perfect. Be your own advocate. A one page bullet point type history is very effective. Good luck.