@srm. Ugh, this Covid pandemic sure compounds issues with being able to have the assistance you need to get through this period. I sure hope your white blood count raises soon. I’ve never had radiation but I know for chemo treatments, if white blood counts are super low during neutropenia they are boosted with an injection of Neulasta. Wonder if that’s an option for you?
The fear is with such a low count, the body is really a target for any infection. Until your WBC is back to at least low end of normal it will be hard for you to beat this mucositis. Not trying to sound discouraging but this is what I was told by my transplant team. And they were spot on. The second the WBC started going up, within a day, I was 90% better. It was dramatic.
You are to be admired for coping as well as you are! Brutal is a mild word for what you’re enduring. I hope you get some good news tomorrow with your oncology appt and some help with countering the side effects of that mucositis. Will they be able to tell you if the radiation treatments have worked for the cancer?

It will be interesting to see what your blood tests show regarding your WBC, hemoglobin and platelets. How long have you had the shortness of breath? Are you also low on energy?