You might need to see a dr to get to the root of the problem...do you think it might be thrush-related? IN which case some swish-around-your mouth drops might be good, otherwise there are some good lozenges you can get on a script which are both antifungal and antibacterial. In the meantime you might get some relief trying to eat by using a mouthwash like difflam which will numb the pain so you can get some soft food down.

In the meantime, concentrate on soft cool energy-dense foods - scrambled eggs, smoothies, chuck a bit of extra skim milk powder or cheese in to boost the calorie content so you can eat less but not be so hungry.