Severe COPD and Interstitial Lung Disease

I was diagnosed several years ago with COPD after 40+ years of smoking. In the subsequent years we have learned I have 4 or 5 interstitial diseases including Interstitial Lung Disease. The two have been about equal but recent testing showed the interstitial is much worse than the COPD. I would love to know if anyone else has this problem and what the effects of the interstitial side are. I have been on O2 for years but just recently I have gotten so bad that I can barely pull 91% while sitting and on my home concentrator. I had always been able to pull 90% without the oxygen. That's how much worse it's gotten and walking is almost impossible. Everytime I get up & walk around I drop down to 80%, even while on oxygen. It's getting harder & harder just to breathe. Would love to hear any comments or advice.