In reply to dannygale:
Sounds like a ganglion cyst if it's like a pea on a stalk, also known as a bible bump as hitting it hard with one was the preferred treatment once upon a time.
I would go get a doctor to look at it, if it's not this then it could be fluid in the joint from overuse of the crimp or a stress fracture from slapping plastic hard down your local wall.
Try the usual rest, ice, compression and elevation for the interim period before you get it checked over. Avoid all forms of work, cooking and cheap beer, treat as you would for man flu.