Loose stools are most often caused by overfeeding.
You say your checked quantity? On the back of the bag? Most often this is too much food.
How much are you feeding puppy? I suggest you cut back by 1/4 cup at each feeding and see what happens. A 4 month old puppy would need about 1 1/2 -2 cups in total per day.
Are you feeding the Large Breed Puppy? Do not feed the Adult Orijen....calcium/phosphorus ratio is too high for a puppy.
Gina