I've had a bruise-like issue underneath my thumb nail for the past two years. It sometimes throbs painfully and it is very sensitive to touch - it hurts to press on it. It's at the base of my nail near the cuticle. It's slightly purple. What is it?!
Bruises can be a result of a lot of things, but for fingers it's most commonly trauma. Did you hit your hand recently? I can also think about splinters getting stuck down there, maybe small enough that you can't see it. If you've been suffering from it for a while, there may also be infection and it may not be bruised, but in fact swollen.
I suggest you go see a doctor, a real check-up would be better than what anyone here can do for you.