Just see if there are any ulcers on the left side of his tongue. Ulcers are the most common cause of pain in tongue.
It might have been due to a bite from teeth/ sharp teeth/ viral illnesses/ oral thrush/ aphthous ulcers
You have not mentioned about the duration of usage of flovent
After usage of flovent- every time- you should tell your child to rinse his mouth. Else there are chances of developing oral thrush (Fungal infection
). This happens more with long term usage of flovent.
You might see a Pediatrician
and get him treated.
For pain you may use gels like zytee till you see a doctor.
Hope I have answered your query.
Wish your son good health.