I lost a lot of weight & then was diagnosed w/ MRSA and once it was under control, I put the weight back on.
I'm not suggesting he has MRSA, but has he had a sputum culture done to see how things are in his lungs? It could be possible that he's picked up an infection or something that needs to be treated.
I don't know why I lost weight and maybe it wasn't related to MRSA, but I have to guess it was related, since I hadn't done anything differently (except cough more).