A few questions,
How old is Nookie Monster?
Why is he on those medications?
Cephalexin - antibiotic, for what type of infection?
Prednisolone - steroid. what inflammatory condition?
Phenobarbitol - anti-seizure medication. Epilepsy? when did the seizures start?
I don't suppose you can take a picture of the area? I realize that is a difficult site to photograph.
Yeast infection would be unlikely within the mouth. They are common on the outside of mouths.
Christopher A. Lee, D.V.M., C.V.L.S.
Promoting surgical options and pet comfort through the use of lasers.