Re-read your first post... Separation anxiety right?
There are a few things you can do to help Niko out.
Have you looked into those plush animals with a heating pad and a heart beat? He's younger than desired (sorry, but it's going to play a huge role in his development and how you should "raise" him) which means he'll need more reassurance and extra help from his new mom (you) that he's safe, protected, and part of a pack. The plush can help simulate mom and litter mates in his new home.
Also, make a special place just for him in case you already haven't. An expen worked so well when I got my yorkie. Granted he was much, MUCH, older than your little one when I got my pup, but I think all dogs crave that safe place that is all theirs. It will be his safe place, and it will help with potty training.
