Hello, For The Past 2 Days My Left Thumb Knuckle

Hello, for the past 2 days my left thumb knuckle (2nd one from nail) has been giving me a little pain, tonight after work it seems to be getting worse, after looking & checking for swelling I notice that it is quite out of shape to my right one, it seems to come out at an angle? I have no explanation why this is as i have not suffered an injury, it just started to hurt all of a sudden. Can there be a simple explanation?