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Congratulations on your new addition(the puppy, not the worms!)
Although it is more costly, you should take him to an emergency room for treatment if he is not eating or drinking, or if he is, if he cannot keep the nutrition inside of him. At 5 weeks, he should still be with his mother.
You might find a vet who will look at the worms abd run a fecal exam on his poop today, but that is not very likely unless you are already established with that hospital.
OTC products can do more harm than good, especailly if he is anemic and needs further treatments since he is so young.
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After reading your note I am thinking what a lucky puppy!