Hello Breen,
I cannot for the life of me remember the name that some lumps are referred to. That is to say the benign ones, that you can get on your arms or back. They are like a little lump of fat, that is how they feel anyway. I have one on my arm which has been there for a least 5 years. Does not trouble me at all, don't feel anything (pain wise), only know it is there when I rub my arm! My GP did say it was perfectly (h)armless, and told me its medical name, but lack of brain power, stops me from telling you!
Having said that, all mysterious lumps and bumps should be looked at, to ascertain that they are 'nothing to worry about'.
Get it checked out, if only to ease your mind...
n00dles xxx