Hi,
There are so many things it could be. Without seeing it, it's impossible to tell.
You need to go to a dentist or medical dr and have it checked. Period! It could be infection starting at the root of a tooth, it could be an infected lymph node, sinus infections or something else entirely. All need medical or dental intervention.
Evaluation is a must for any lump found where it doesn't belong.
I urge you to make an appt with your dentist and let him/her check it out.
My best to you,
Gellia