I went through this with my cat, Andy, when he was a little kitten. He used to sleep with my daughter and she practically had to sleep totally under the covers because he was such a nibbler on any exposed body part! We really were at our wits' end when he gradually just grew out of it. I can't say that we did any one particular thing, but it just stopped. Today he is the most lovable sweet lap kitty you could ever meet. Try and hang in there. I know it's hard but hopefully it will pass.