My Teddy dog walks with his back hunched. Holding him hurts his neck.

It may be calcium deficiency. You can buy some calcium tablets for the puppy, one a day.

Let it get more sunshine.

Teddy's calcium deficiency is not only manifested by always hunching his back when walking, but also by double rows of teeth, poor leg shape and splayed or splayed forelimbs. When you stand, your toes will be apart, just like a duck web. If you don't stand straight and don't like sports, your nose will become lighter. Calcium deficiency in adult dogs is generally characterized by hot flashes, irritability, easy fracture and dislike of exercise.