I've been getting 5FU, which is the same as Xeloda except rather than a pill, I get the chemo infused directly into a catheter in my arm over the course of a week.
Anyway, I've experienced the mouths sores, and they really do suck! My oncologist lowered the dose by about 10% for later rounds, but that first round with the mouth sores was tough. One thing that helped me was a special mix my hospital prepares; they combine Nystatin (an anti-fungus medication) with lydocaine to freeze the mouth and throat and provide some comfort, with some kool-aid thrown in to make the taste bearable. After swishing the mixture, eating is a lot easier for about a half hour or so.
One thing that I was able to eat even with the mouth sores (though it was difficult) is Ensure milkshakes. I tried to eat 3 or 4 a day. Also ate Yogurt. Almost everything else was impossible. By the end of that 1st round of chemo, I was on Tylenol 2 to help me deal with the pain in my ears, mouth and throat from the sores.
After all the aggravation of that 1st round, I went online to look for preventative measures I could take to help ensure I didn't get the mouth sores again. I found recommendations for non-alcoholic mouth wash and for drinking lots of ice cold water. I have been swishing with the mouthwash (crest makes a non-alcoholic one that I like) and drinking plenty of ice cold water ever since, and I haven't yet had any mouth sores in the 6+ rounds since the first one.
Finally, I have also heard that chlorhexidine might be helpful, but I've never tried it myself.
Now, for the diarrhea! I try to eat a high fiber diet and it also seems to help some. I eat mini-wheats for breakfast, and have yogurt with granola on most days. Sometimes, I also eat some high fiber bread. I think some amount of discomfort in the bathroom is inevitable, but I've noticed that my own bathroom trips have been more manageable with the high fiber diet.
Hope that helps!
-T