Continue immunotherapy or stop

I am a 73 yr old male. I was diagnosed with stage 2 NSC squamous cell cancer upper right lobe in May. The thoracic surgeon did not recommend surgery because of the COPD and said guaranteed I would be on O2 full time after. So, my oncologist said 7 weeks of daily radiation and 6 weeks of carbol-taxol chemo. The PET scan some 6 weeks after completing chemo/rad showed the the uptake values went way down (from 21 to 6.7) whatever that mean. In any case the oncologist was very happy and said let's start immunotherapy (Imfinzi) once a month for a year. After 3 treatments I developed pneumonitis and my SOB got much worse. He stopped the immunotherapy and put me on prednisone, 40mg/day for a week, then 20 then 10...well, I had to stop the prednisone because for me it was like taking poison. I had very bad side effects (but it did clear up the pneumonitis) and the doc tapered me off pred in 4 days. That was a relief to finally quit taking the pred. In any case my SOB is back. I am worried that the immunotherapy has caused permanent damage to my already diminishing lung capacity. The prednisone made darn near crazy. I am going to see my oncologist next month and just want to stop the treatment. I feel like it has made things worse. Can anyone relate to this dilemma? Thanks in advance. Bill