I've got one that sounds the exact same actually. I've had it since I was 21 (30 now). its not got bigger but it used to get real sore some years back when i'd eat lots of cheese
Its not so much a problem now - the pain I mean.
i went to a gastroenteroligist who had a few prods and asked me some questions. He told me to lay off the cheese and not worry about the lump. i thought he was going to have to stick one of those camera scopes down my gob to look at it.
I was nervous it was an ulcer or maybe even cancerous, hence I got it checked out.
So there you go - £80 for a referral and he says dont eat cheese.
Hope that helps