Bruised knuckles?

[OneTwoSkipAFew99~100]

I've been having some kind of problem with my fretting (right) hand, recently. The knuckles on that hand are faintly bruised and I feel minor pain when I open and close my fist, or when I knock on a door with that hand...things like that. It hasn't affected my playing any, as when I warm up properly I don't even feel it. I have been playing an awful lot as of late, and I was wondering if anybody else has encountered this problem! If so, what did you do about it?