Talk to Ent Specialist on Child Mouth Blisters

Assalam u alaikum.my son age 6 years has issue of blisters(chaalay).After every few days a new very small blister appears in his mouth.Sometimes we can see blister and sometimes theres no blister but child complains having pain.It must be mentioned that from last few years he hardly eats any thing with spice.Doesnt eat meat etc.His diet is reduced a lot.Apparently his tongue is normal.He also has cavities in teeth...kindly advise.Secondly he has large adenoids and tonsils so can these mouth related issues be due to breathing from mouth instead of nose...