DD, has any of the doctors he has seen been a dermatologist? According to my Taber's, lichen planus "usually occurs in otherwise healthy people who are emotionally tense." I think I once had a form of it on the palms of my hands, which eventually went away. That was quite a few years before hep C diagnosis, although I had already contracted it. Has he been on antibiotics for an extended length of time? If so, it could be a yeast infection that is caused by antibiotic treatment. The only other poster I can recall with mouth problems is Charlie's wife. She has autoimmune hepatitis.
The Taber's further states that treatment is therapy for the anxiety and local ointment. "The disease is self-limiting but may last years, or recur." I would have him see a dermatologist, if he hasn't already. Also, provide straws for drinks.
I have a feeling it's from a combination of stress and the increased Xifaxan dose. Good idea to see an infectious disease doc. Let us know what he has to say about the situation.
DD, I'm glad you got confirmation of the problem and I hope that the Flovent works for your hubby.
Please do keep us posted, and also let us know the results of the scan.