Is this on the palmer side? Somethings to consider from a reflexology standpoint: the middle finger is the healing finger, because it is the left hand it is the healing finger of your present (now), if it were the right hand it would be the healing finger of the past. The index finger is your communication finger, it is your communication finger of the present. I always get pain in my communication finger or toe on the left foot or hand when I am struggling voicing something to someone. Perhaps you are struggling communicating with someone in your practice? A client?