You are an amazing and wonderful daughter. Get a second opinion. Ask for a CT chest scan. If you live near Mayo Clinic or a similar medical facility have you thought about going for a second opinion?
I ask this because of my history of lack of treatment by a general physician in a small town and a team who did not know how to begin to properly diagnose or treat my symptoms.
The most important thing is your mom’s Quality of Life, as yours too. And as for Mayo Clinic, they saved my life! Trust your instincts. Bravo to you for being such a kind and caring son!