Hi. Last Night I Was Outside For A While, In

Hi. Last night I was outside for a while, in the freezing cold, and when I came home I had a small blue mark between my ring finger and my pinky on my right hand. I tried to rub it off as I thought it was blue marker or something of the sort, but got a lot of pain running through my hand for approximately 5 minutes. When I awoke this morning, I had a bruise around my knuckle and I have no idea what or how it got their. I did not punch or hit it off anything, and I'm completely clueless to how I got it. Have you any ideas of what it could be?