Good morning, lilianna, you may have what has recently been recognized as "dry bronchiectasis" which means you produce little mucus. I believe the accepted course of treatment for it is to use saline & airway clearance, but not to be too upset if it is not productive. At least you are keeping the tissues moist and the saline staying there makes your lungs inhospitable to bacteria.
Do ask your doctor about 7% as it is even more lethat to MAC than the 3%.
Sue