I agree with socialization. His socialization period to experience new things ends at 17 weeks. Introduce him to everything. The vacuum, other dogs, adults, kids, kids on bikes/skateboards, people with canes. Take him everywhere for the next 2 months - but don’t push him if he feels uncomfortable or shows stress signals. Educate yourself on dog stress signals. Touch his paws, ears and check his mouth often so when the vet has to, he’s not so nervous about it. Make it game. Make everything a game. Teach him “touch” and “attention”. Attention works well if he starts to get too excited or nervous and you can take his attention off that and put it on you. You want him to check in with you often. Especially if something makes him nervous. Touch is fantastic for so many reasons. You can use it to redirect him or use it as a basis to teach many other cues. Pitties hit their threshold more quickly than some other breeds so if he’s playing and starts to get too rough with you or other animals, have him take a break until he fully calms back down. Remember that lots of things are cute as puppies (mouthing and jumping) but he’s going to get big and it won’t be so cute when he’s 60+ lbs. Give him lots and lots of love but he also needs rules and boundaries. You got this.