Hi welcome to health care magic forum,
Tonsils are lymphoid system
which guards aerodigestive tract from common infections. But some time it get infected and cause sore throat
,pain during swallowing food and mild to severe fever.
But what u described for ur son blisters with burning and itchy , it could be less likely to be tonsillar infection.
Sometimes an aphthous ulceration over tonsillar area may present with silmillar sings and symptoms.
you can give the medications to your son if you find confident on the doctors .
If not please take a second opinion
with an ENT specialist