Licking is a self-reinforcing behavior. Your dog may be doing it to make itself feel better. You can try distracting your dog with toys/games and encourage it to chew on appropriate things (chewing is also a self-reinforcing behavior). These behaviors often become obsessions. The key is to find something it loves more than licking.
As for why it is licking you, it is because your dog loves you. I'm not a big fan of licking either. I have a dog that would clean out your ears and nose if you let him. I try to give him affection while positioning him away from me. If I'm busy and they are licking me for attention I just move slightly and they stop. Once they stop, I give them attention.