Hello Roxs-sounds like my dad had the exact same complications as you (severe mucousitis-hospitalized-delayed tx) What worked for him was staying with the pain meds so he could eat and drink.
Are you still on any strong pain meds? My dad's mouth was falling off in his mouth. Happy to say that he is eating everything 3 mos out.
Be paient, keep with some pain meds to take the edge off-drink the lido. You will make it though this-it is amazing how the body bounces back. He was able to completely wean off the pain meds-
Stay strong!!