First, Congratulation on your new dog!
So the thing here is that your dog have been deprived of attention by his last pack leader ( last owner), So he have forget some of is basic instinct of being a pack animal.
You have to work on creating a deep bond with your dog.
Here is a great article that will explain you how.
WOOF! . Tips from Matty . Bonding with Your Dog | PBS
Good luck.