Poop eating is not uncommon in puppies. It is a nasty habbit for sure, and stopping it is a good idea. If the dog looks otherwise healthy, I would not necessarily run him to the vet. Since he is very young, when was he last wormed. Keeping poop picked up and the puppy properly wormed is important for his health.
i find keeping an eye on a pup and leashing helps with stopping them
from eating poop.
Both of these are good advice. I don't feed based on the bag's recommendation. I base it off how the puppy looks. I try and keep them on the leaner side as well.
Eating poop can also be caused by a missing nutrient in the food. Supplements or changing to a high quality food can sometimes help. Other than that, just keeping the puppy from doing it is the key. Definitely check for worms.