I'm sorry I don't agree, my DDB puppy was extremely snappy as a puppy right up until she was almost 6 months old I wouldn't have dreamt about getting a behaviourist in at such a young age (normal puppy behaviour in my opinion) I would say she was still very much finding her feet at that age as to regards still getting to know us as her family & having to adjust to getting used to living in a multi dog household.

It IS behaviour she HAS NOT continued to express into her adult life, I would tend to lean towards thinking you don't seem to have an awful lot of patience with him whatsoever - probably WHY he's doing it in the first place.

And by lord if that isn't a behaviourist after your money, I don't know what is