Welcome Preaux, It's uncommon to find cancer in the retromolar trigone area.
HPV is mainly in the oropharynx, 90% of the time, and usually doesn't present itself with an ulcer like tobacco or other carcinogenic related cancer does. Your symptoms definitely need looking into by an ENT, as Mr. T suggests, but it could be many other things besides cancer, like an infection, salivary glands infection, etc. Good luck.
