[cypher]

If he's put on some weight then that is at least a one positive sign!
That's a shame, if it's happening in cycles then I guess the only thing is to go back to basics & try & consider anything & everything that might help or hinder his recovery.

Just a few things that come to mind, maybe others will think of something else that could be a factor...
Are you still using the fitch for substrate?
What else does he have in his cage? Anything mites may be hiding away in do you think?
Does he have a sand bath?
What supplementary foods & main mix are you using?
Have you tried the evening primrose oil or something like the Omega oil & did you stop the cod liver oil?
Has he had any probiotics while all this has been going on?
Is there anything in his cage or environment generally that could possibly be causing him stress?