Thanks for posting your query.
Your son c/o recurrent aphthous ulcers
The cause of occurence of lesion has to be ruled out initially.
Since anxiety can be a predosposing factor for occurence of ulcers,i would advice your son to avoid anxiety as well as stress.
Take nutritious diet as well as plenty of fruits/fluids.
Maintain oral hygiene
Rinse your mouth after every meals.Hormonal
imbalances has to be evaluated and treated.
If symptoms persists,please do visit a dentist
Hope this helps.