as you already said, biopsies do not cover all types of bacteria/fungi
if it is indeed a type of fungus, maybe it does not want to be discovered :D (sounds weird but you never know... in fact some biopsies indeed show some fungus there but in most cases, antifungal creams don't help but in SOME cases they did, i heard of 2 by now...)
so, you are the creator of exfoliativecheilitishelp?
are you still suffering from the condition?
does sticking to the diet completely stop peeling? or did it return anyway?
were you a lip biter/licker/picker before you developed it?