I am sorry to hear you are going through this. I by no means am a dog trainer but a few things come to mind. 1) Is he getting enough exercise? Do you take him out for walks, run around the yard, etc.? 2) With you being as you put it, "anxious" he senses that and then he becomes afraid. One way of dealing with that is to become aggressive - its a defense mechanism or coping mechanism for them. I don't fully agree with Caesar Milan's teachings, but I do feel that the pups need to know who is in charge and with you faltering, he is not sure. Similar to what the others have said about having a "talk" with other aggressive dogs, maybe he needs to have a talking to, but you need to exude confidence. I am "friends" with Victoria Stilwell on my FB page and she has some great methods of training. 3) Maybe your pup is bored and needs more stimulation. 4) If all else fails, put him on puppy Prozac - some dogs need it. When I was growing up, we had a Pomeranian/Poodle mix and he needed to have some "Prozac-like" drugs on occasion because he was so high strung and out of control - and he was a biter - bit my uncle, my mom, brothers - but he never bit me - I guess he thought I was the pack leader
Whatever you decide, I wish you the very best.