My pit puppy is about the same age, and I’ve had puppies in the past. Honestly, they love to nip, chew, and bite for a long time. All you can do is keep working at it and telling them no.
I also would like additional advice on how to train a pit puppy not to bite, as I’ve only dealt with other breeds in the past. But I wouldn’t worry excessively about what is, in general, a normal puppy habit.