How much are you feeding him? Maybe too much? How old is he? Puppies do go more frequently than adult dogs.
Also he’s still a puppy, eventually he should have (on average) 2 bowel movements a day, usually an hour or 2 after meals.
I would consider Purina Pro Plan sensitive skin and stomach. Grain-free doesn’t agree with all dogs, plus it’s just a marketing gimmick. What you are feeding may be high fiber.
I would try feeding a smaller amount of food divided into 3 or 4 small meals with a splash of water added and a spoonful of something soft like chopped cooked chicken (use less kibble to allow for the protein topper).
At about 6 months I would go to 2 meals.
Ideally, if you could take him out every 2 hours to the location you want him to eliminate, he will be housebroken in no time. I know this is not always possible but take him out as frequently as possible, especially after playing and eating, brisk walks may help
