Mouthing and nipping are two different issues. Mouthing is a communication skill to get you to do a particular thing. Less pressure, less annoying, but still not particularly charming.
Nipping is a puppy thing; it is interactive and playful. Nipping puppies are bossy and manipulative and need a firmer regimen.
Mouthing is often an attention-getting behavior. If your puppy uses it to communicate a need to go out, respond. If, on the other hand, your dog mouths you for a pat, ignore it.
If he becomes too annoying, get a water spray and spritz him discreetly in front of his nose, hiding the spray in your hand and spritzing as you avoid all eye contact, comments, or pushing.
When you use the spray this way, you are performing a cause-and-effect correction rather than interactive discipline. Interaction involves eye contact and physical manipulation – not good.
Cause-and-effect corrections result in unpleasant reactions that your puppy will try to avoid.
Nipping is another one of those puppy things that you need to refocus.
When your puppy still hung out with his litter mates, he nipped during play and to determine his rank. He also soft-mouthed his mother affectionately.
When you bring your puppy home, this behavior continues unless you undertake some Puppy training.