You need to take your dog to an emergency vet NOW! I'm sorry but I think your puppy has parvo or distemper. (I'm sure I spelled them both wrong, sorry) I had a puppy that did the same exact thing that I had gotten from the humane society and when we had him checked it was one of those two and he had to be put down. I'm sorry to tell you this and I hope that is NOT what it is but if it is he is suffering and very, very sick. Please get him checked so he won't be in pain! Thank you and good luck to you both!