I would really advise that you go see your GP and see what they say. Better to be safe than sorry, even if it turns out to be nothing major :)
You need an immediate evaluation, preferably at a teaching hospital, and not a GP. The history is important. Did you just notice this, or did it develop suddenly? All growths are not malignancies, but all require immediate attention. That means as of yesterday, and not an appointment with your GP four weeks from now.
Go to a doctor. Lumps are BAD