VERY aggressive behavior with chi/yorkie male puppy?

My chi/yorkie is 5 months old. He has gotten very aggressive, vicious, lunging at me, biting my hands & fingers. I took him to the vet, everything is ok. He will start Obedience Training in a week. I cannot get the halter on him, he goes "kujo" on me. I've never had problems like this with any other dog I've ever had. I at the point of almost being distraught. Any help/advice would be much appreciated. Thanks, Mary