How can you tell if a puppy has worms?

Most puppies do have worms. The runny poo with the blood could be one sign of worms, also, if the worms are very bad you will actually see them in his poo. Swollen looking pot belly and just an un-thrifty, un-healthy look can be indicative of worms or a 100 other problems. The vet can tell you for sure and will most likely give him a dose of de-wormer. As for him eating his poo, that is just what some dogs do. I have five dogs and two of them are dedicated poo eaters. I've fed all my puppies Pedigree puppy food with no problems. You'll hear a lot of people bash commercial dog foods but they've always worked well for my dogs. (I prefer Pedigree over some other commercial feeds because it doesn't have soy in it)