just give him time he may be afraid of going back to the shelter or the other place he lived (maybe his lack of training resulted in punishments that stays with them for a while
when I got my puppy she was 4 1/2 months old and they said their 2 & 3 year olds were not taking care of the puppy (what a shock) then when I got the puppy home she was terrified she could not go out side she would not go out for a walk I would put her leash on and she would cry Then I would walk her around the block or should I say carry her around the block and I could not get her to go into the car for a Petco shopping spree she seemed terrified
Other than her fear of going outside she was perfect She is extremely affectionate and seemed to like us but the going outside stuff was weird even when I went with her I emailed the women that we got her from I then found out we were the 5th family to have her in 4 1/2 months, No wonder why she would not go outside she was afraid of moving again
Now, 3 months later she Loves going to Petco She goes for long walks we walk to get Coffee every night it is about 3 miles round trip She still likes to be carried some times when we walk ( makes a lot of people laugh at us ) but she now feels at home She is still a true lap dog and trusts us totally now
When she had her surgery she still wanted to walk because that is what we do Enjoy your pup we do !