I'm glad he went to the vet. I hope the prednisone will calm down his lungs so he doesn't cough anymore and that it is only inflamation that goes away. Let us know how he does in a few weeks time. Good luck.
Thanks much for your help. Doc took xrays. Says there is a weird pattern going on in his lungs. He can't tell at this time whether it's inflammation or something else. My cat had a malignant tumor removed from his ear 5 yrs ago. The vet says that kind of cancer also likes to go to lungs and stomach. We are doing another xray in three weeks to compare. He gave him a shot of pred to give the lung tissue a rest from what we hope is just inflammation in his lungs.
It still could be a hairball - sometimes they take quite a long time to get up. Have you tried any hairball remedies? There are some that taste like fish now and they will lick off your hand and then there are some "treats" that have it inside them.
I am glad you are taking him to a vet too in case it is something else or it could be a nasty hairball that needs vet treatment. Three weeks is a very long time. Hope all goes well.