It is natural that your puppy will try and mouth you. Their adult teeth come through at 14 weeks which can be very painful for them (and you too if they are mouthing)!
Distraction is the key to stopping your puppy mouth or bite you. Using a toy can help to distract you dog as if they are chewing the toy they cannot chew you.
In addition to using a toy as a distraction, providing you puppy with something to chew on can help with the teething. A rawhide chew may help but don’t leave your dog unattended with it. To get your dog to lock on to the chew spread a very small amount of honey on it. You could also try using a pair of old shoes with the laces removed or latex toys which have a bit of give in them.