PF and symptoms

I've been officially diagnosed with pulmonary fibrosis for about a year. I'm not on oxygen or Ofev yet. The diagnosis came after my second knee replacement which went well but about a month after that I got pneumonia and that lead to the diagnosis. Prior to that I was told I had interstitial lung disease. It wasn't really talked about being fibrosis. I was rather run down and out of shape from two knee surgeries in a little over a year so I was told to try and exercise after the fibrosis diagnosis and that would give me more strength and endurance. So I have purchased a NuStep machine so I can exercise every day. I've been doing that for almost 3 months. However I still am not able to stand for an hour while cooking or cleaning. I sometimes feel like I could faint. My blood oxygen level is over 90. I've read other stories of people who are able to walk up to 2 miles and play golf. There's no way I could do anything like that. I can walk maybe 10 minutes at once and then I'm wiped out.
Does anyone else have symptoms like this? Is there something that the doctors are missing? I've seen a cardiologist and my heart is good so that isn't a problem. I'm rather frustrated!
Any suggestions would be appreciated!
Thanks,
Carol