Most of the stuff you buy over the counter here in the US does NOT work!
You really should take him to the vet along with a stool sample. They can check the stool sample to see if there are any worms present.
Most vets ask you to bring in a sample when you take your pup in for its puppy shots. Have you taken him in yet? It is also recommended that you take him to your vet for a check up within 48 hours of purchasing a pup for a health check. Any concerns or questions can be asked then also.
You didn't say when you got your pup, have you taken him to the vet yet?