Sannira, I was recently treated at Mayo PHX for my prostate cancer, with Photon Radiation (38 sessions), after getting a 6-mo shot of Lupron. No chemo, and I have my first post PSA test coming out the end of next month. Felt, and feeling, good through it all. Continuing to exercise (treadmill, some weight machines) has certainly allowed me to sustain better thru it all, as well as have my energy.
My wife cared for her father the last two years for his AML cancer. He passed away last summer. While he didn't have chemo for PC, he did have chemo. During that, one particular time, he once got mouth sores, and like you stated, wasn't able to eat well---blending food, but really not having much of an appetite. Nothing they gave him was helping. In fact, after getting too many antibiotics, he actually developed C-Diff, but miraculously, he was able to overcome that within about 8-10 days. Since nothing was helping his mouth sores, tho, my wife came across a particular remdy that he was more than willing to try. For several days, he would swish about a tbsp or so of Olive Oil around and around in his mouth for about 20 minutes, a couple of times a day, BUT, then spit it out without swallowing (it was said you could also use coconut oil...he preferred the olive oil), The theory is that it can grab germs, bacteria, etc., along with leaving behind some healing properties in the process. On the third day, he was feeling good enough to eat some softer foods, and by the 4th-5th day, his sores were gone and he never had any more problems with them after that. He continued to do the oil-swishing about 1 time a week, just for better mouth health. (For info---you are to swish, rest it there, swish in and around your teeth/gums, rest it some more, etc. One doesn't have to swish constantly.)
You can do a search for Oil-swishing and determine if that might be something you would like to try. In both their opinions, it couldn't hurt....and it helped quicker than anything else.
I hope you feel better soon, whatever you do.