I would go a step further than David and recommened that you have your entire pain management program evaluated for efficacy. Morphine is typically given for "short term" pain relief and also for breakthrough pain. You will also need to be on a "long term" pain med, such as Fentanyl or Morphine time release patches. RO's and PCP's are terrible about prescribing these - talk to your MO or get a referal to a pain management specialist. Pain control is a basic patient right - demand it.

It is early for mouth sores, they typically start to show up in the third or fourth week. The yeast infection (AKA candidiasis) or Thrush, is common when the pH in the mouth changes for any reason, dry mouth, etc. This is probably the main source of your mouth pain. It would be a burning sensation, similar to mouth sores. You also didn't mention chemo - some chemo drugs, especially Cisplatin will exacerbate mouth sores.

Whatever you do, do NOT stop treatment. The odds of survival are greatly diminished if you do.

By the way, many of us here were misdiagnosed or diagnosed late. In the scheme of things many doctors (and dentists) never even see an OC patient during their entire practice. SCC is relatively rare - your form of OC I can count on one hand in the 8 years I have been here.