Soft palate blisters...
If I have read your post correctly you have had radiation therapy that included your soft palate and uvula area either directly or indirectly via scatter radiation.
Radiation and Scatter radiation damages the outer layer of mucosa. Minor salivary glands mucous and serous are located in your soft palate forward of your uvula. These glands aid in lubricating things (food) you intend to chew and swallow and provide some enzymes to help break down food.
When minor salivary gland orifices are damaged they sometimes become covered by the overlying mucosa rather than the minor gland duct openings due to the fact that mucosa forms faster than gland duct tissue. When theses minor glands are stimulated they produce fluid and if the gland duct is blocked the fluid builds up underneath the mucosa and appears like a blister. These can be painful, until they break and there can be many or few.
The duration of this occurence depends on the area that was damaged and the amount of damage this area recieved. In most cases this situation will resolve itself.
Drinking plenty of fluids and chewing food very methodically can reduce the severity and length of the problem.
Cheers,
Mike