Hope you either photographed the worms on your phone, or saved them, or there may never be a diagnosis. Did you see the worms in the stool RIGHT AFTER your dog pooped, or later? Because the worms you are describing are not worms at all, but fly maggots, commonly found in dog stool as little as 12 hours after pooping. There are no short, 'round worms' in dogs that are not thin as a hair (hook worms are fairly short-though much longer than a tapeworm segment- but really skinny and wiggly; round worms are long, usually curled in a circle and look like white earth worms; tape worms are segmented and flat, though most people only see the individual segments which are about the length of a piece of rice but distinctly flattened, and die soon after they come out, eventually drying into a light tan color, the shape of a sesame seed, only a bit flatter; whip worms are also very skinny though can't say as I recall exactly what they are like as they are very rare here in California). WE often get clients complaining of their dog's having stools full of worms, but when they bring in a sample it's full of maggots, not worms. Having a stool with tapeworms in it, however, is often a random occurrence, even in dogs with a lot of tapeworms inside. Dogs can have have tapeworms that only shed segments so intermittently that owners only glimpse them once every 3-12 months. So the worms not being there every other time you check does not mean they are gone. But it also fits the maggot scenario, as flies may only lay their eggs in a stool every now and then.
