Facial lump very flat and raised about 4mm high

I am not sure what category this question should go in as there was nothing on "lumps"
My son has a flat lump on the right side of his face, it is on his face just in front of his ear...the bottom of the lump is around the bottom of his ear. The lump is very flat and raised about 4mm high and about 30mm long, 20mm wide.
It appears to be solid (more so at the top end) and hard but can be moved up and down - there is no change in skin color. It is slightly sore and has been on his face for a couple of months.
He is always putting off to see a doctor to see what it is and has been saying that it is related to his teeth problems...he has recently had nine tooth removed and some of these teeth caused him a lot of pain before they were removed.
I would appreciate any suggestions as to what this 'lump" may be and what needs to done about it.
Many thanks