It is more difficult to own a puppy that was an only puppy, or one that was taken from his mother too soon. They miss out on a lot of very important training that way. By your dog not having littermates, he has never learned not to bite. It's rather like an only child that has never played with other children - that child would have no concept of sharing toys.

Here is link to a training site, with many good articles on puppies with chewing/biting problems: http://www.uwsp.edu/psych/dog/lib-Puppy.htm#pchew