Maybe you should ask the doctor about a pain patch. They come in different doses and last about 5 days at a time. I had them but forget what they are called. I was on the pain patch and used Oxycodone and percocet for break through pain. Based on my experience and what I have read here, around the third week of radiation is when a lot of the side effects kick in - loss of taste, build up of mucous, mouth sores, pain increasing, tiredness. I believe there needs to be better pain management between the Dr and your Dad. Also, he may want to take a stool softener along with his pain medication. Pain medication can cause serious constipation. I bought stool softener pills up at Walmart and took them daily.

Does your dad have a peg tube? How does he eat? How is he doing eating and getting proper nutrition? Has he lost a lot of weight? Getting nutrition is very important to the recovery and healing process.