You're hurting, that's for sure. ((hugs)) Wish I could make it better.
Gonna ask a question, because this is something I didn't find out till nearly the end of my treatment, and it would have saved some pain and, well, pain ... Do you have fillings? Those will cause radiation scatter, depending where they are. When I hit the point where I was crying in pain putting on the mouth guard (last couple weeks of treatment), they finally told me about this, and turns out there's some dental wax they can use to help cover those teeth which helps prevent some of the scatter (and thus some of the sores) and also it eases the fit of the guard a bit where it ouches. So ... that's something to ask about, and see if it's an option for you, especially if you do have fillings that could be causing extra issues.
(My nurses were nice ones, but they just didn't tell me stuff unless I asked ... and I didn't know to ask, of course, since I'd never done any of this before. Maybe my pain can be your gain.)
Another thing ... if you're having bad anxiety with the mask (and yes, that can be terrifying!) ... see if there's a low-level anxiety medicine you can take. I know my psychiatrist and I upped my anxiety medication for the duration of my treatment ... no questions asked. (He's good like that ... we both knew it was going to hit on a LOT of my anxiety issues, so we just upped my prescription amount that I could take as needed.) No need to add suffering on top of misery, if you can do something about it and this is an option that's okay to you. (Not everyone is okay with anxiety medicine, and that's fine ... but if you're willing to look into it, go ahead and ask. Worth a try. Worst thing it does is make you a bit sleepy, and since you need to rest to heal up, that's not a bad thing.)
Not sure on ideas for the rest of it, but lots of sympathy. And ((hugs)).