Is this a sign of oral cavity cancer?

so i had this painful ulcer right behind my wisdom teeth on the top left side of my mouth.. i thought the ulcer was causing the whole left side of my mouth to hurt but now that the ulcer is healing it's still painful to open my mouth. I investigated and found a painful lump on my retromoler trigone (the tissue that connects your jaw on the inside of your mouth). I went to the dentist 2 day's ago.. he checked out the ulcer and gave me an xray to get my wisdom teeth removed but i never noticed the lump then.. should i go back and mention this to him or do you think it will pass with time ?