My heart goes out to you @srm for having to deal with the pain and agony of mucositis and your cancer which prompted the radiation therapy. I had a horrible bout with mucositis myself and it was one of the worst experiences of my life. It was a side effect of the extreme chemo I went through during my transplant experience. I was in the hospital for over a week on a fentanyl pump! You’re enduring this at home? For anyone not familiar it’s like having a million canker sores in the mouth and throat making it impossible to eat or drink anything!

Have you reported this to your oncologist? If it’s continuing to progress this long after treatment you need to be evaluated. There are also pain medications and oral rinses which can help heal the oral mucosa and give you some relief!
When is the last time you’ve had a blood test? If your white blood count is down in the neutropenic level, the mucositis will be difficult to heal on it’s own.

I found this link from the Oral Cancer Foundation with information about mucositis that might help give you a starting point for a discussion with your oncologist on getting this resolved.
https://oralcancerfoundation.org/complications/mucositis/
What have you tried for oral mouth-rinses to reduce the pain?