Reason for reduced stamina?

After several years of dealing with Bronchiectasis, I am finding that my stamina for much of any exertion, especially if it involves any uphill incline, is getting lower and lower. I haven't had many flair-ups and my recent CT scan doesn't show further damage beyond what the original diagnosis revealed. So, I am puzzled as to what to do. I will check with my pulmonologist when I go in next time, but I thought I'd run it by some of the real experts who also live with this issue.

Thanks for any input you might have to offer.