Since change in size and/or pain
in a lump is one of the 7 warning signs of cancer, you need to get
in to see a doctor as soon as possible and determine which it is.
In all likihood it will be a simple cyst and easy and cheap to treat, but you do not want to fool around and wait to find out, because if it is something more, then early detection and treatment is crucial to your long term health.
Not trying to scare you here, but just encourage you to do the Safe thing, and get seen.