Could you have hurt it some other way? For example, back in February I bruised the base knuckle of one finger when repeatedly slamming my car's hatch in -20F temps. It's still slightly tender. Another thing to watch out for is acute bursitis. I've had it in a hip and an elbow. It occurs seemingly out of nowhere, a few days after the event that triggers it, so it's easy to ascribe it to something else. For me, Naproxen kills it quickly.
It could also be that you're simply discovering that no matter how "young at heart" you are, time still takes its toll on your body. I think yours is whispering to you "Lee, switch to a Greenland paddle..." 
