Has he been neutered? Sometimes behavioral changes are hormonal, if not. I would immediately start retraining him, walking him on a short leash, and working on basic obedience with him. You might see if there's any classes available that might help you retrain yourself and him. Right now, it sounds like he is in charge, and you are afraid of what will happen, and so that needs to change. Dogs will pick up on any uncertainty on your part, and take advantage. Start back at the beginning, where he has to earn any praise or treats. I hope this will help.