[JoeyP]

This is a dog's way of showing submission
It sometimes happens with puppies and they grow out of it
but some nervous dogs don't grow out of it

To help what you can do is modify your approach so you're not as threatening

For a while try not to reach down to grab your pup
call him to you and let him sniff your hand first
try and get lower to the ground too
crouch down so you're not so high above him

also watch the tone of your voice
try and be as sootheing as you can when you talk to him