What Causes Pain In Index Finger And Blue Line Forming On It?

I get a sharp pain in my index finger of my right hand. I see a blue line form which I believe it to be a vein. It really hurts badly. After massaging it for about 30 sec or so, the sharp pain goes away. My finger is left feeling swollen, a little discolored in a shade of blue where the vein was and feeling tender. There is still some pain lingering for a few hours. This has happen to me a few times. Any ideas of what it may be? The last time it happen I was sitting in a car during a trip.