Painful bumps on finger joints?!

I've had hard, bonelike bumps on most of my fingers in my left hand since I was little. They are located on the bottom side of my middle knuckles (on the palm side of my hand). I have been tested for everything from arthritis to diabetes by four doctors, and no one can come to a diagnosis. They are very painful, and I cant bend my fingers all the way. It is hard to pick up things, and there are days where my fingers throb and my entire arm goes numb.
I was wondering if anyone else has this problem or knows anything about it. Any information would be appreciated :) thank you :)