Dairy helps neutralize the acidity of tomato based foods. Have a glass of white or chocolate milk handy when trying foods that could be acidic. Beware of Chinese food too, for me it burned worse than any other food. Eventually I was able to eat won-ton soup. Its basically just broth so hardly any calories in there but its great for keeping you hydrated. You probably have seen this already, but it may help others who read this thread.
List of Easy to East Foods. PS... Please push yourself to take more in. Losing weight now means you are not taking in enough to heal properly. I know Im the biggest nag about intake and I probably always will be! Im speaking from experience, I struggled and found out the hard way by being hospitalized a couple times for malnutrition and dehydration. I felt so bad I actually thought I was dying and thats what it felt like. Even if you spent your entire life overweight, it could be years before you have properly recovered and rebuilt your body enough to gain weight. Im now almost 7 years post rads and Im still slim after dropping 65 pounds. Its a real struggle to take in enough to maintain myself. When in doubt, take a 3 more bites or sips and then repeat