Hello, this is Dr. Sara, a veterinarian for nearly 20 years. Congratulations on your new family member! I'm sorry to hear he isn't feeling well. If you haven't already had a fecal sample checked by your veterinarian, I would do that right away. Many puppies that have one type of worm will have multiple types and not all of them can be seen in the poop. Many of them are microscopic. The roundworms are particularly concerning because they can be spread to humans. To effectively treat roundworms, a minimum of 2 doses of deworming medication, like pyrantel, need to be given 2 weeks apart in order to kill all life stages of the parasites. It's also a good idea to make sure that he has been given at least 2 vaccines again parvovirus since that can cause life-threatening vomiting and diarrhea. I hope this information is helpful. I hope he feels better soon.