John, radiation sucks brotha and will burn the hell out of your tongue and cause pain. It could also be thrush which is common, talk to your Dr to see if it's thrush and they'll give you meds for it.

Magic Mouthwash will help, also maybe up your pain medications or just stick to Boost. Citrus (acid), pepper, vinegars bases etc will hurt and anything with them in it will hurt, but it won't last forever my friend, just a process.

Keep hydrated, drink lots of water as we've noticed those that focus on nutrition and hydration have less severe side effects. Focus on high fat/protein intake through treatment (add protein powder and olive oil to your boost) and stick the hydration brother.

Take a deep breath, focus on what you can control which is your attitude, hydration and nutrition.

Keep plugging in here John, we're here to help as we can my friend.

Eric