With my puppy the vet asks for three thumb nail size stool samples taken over three days. This is then examined to see what treatment is needed. This works very well, maybe your vet would do this for you?
It costs aprox 20 Dollars.
Oh the poor little guy! With an infestation that bad, your best bet is to have your vet worm him and do rechecks until you're certain the problem is gone.
I rescued a tiny puppy years ago who had the worst case of mange and starvation I've ever seen. Our vet wormed him twice and we thought that was the end of the worms. Wrong. As we battled the mange with dips and it kept coming back, my vet suggested a heart worm treatment when he was about 4 months old.
I had no idea the injection back then was primarily arsenic. Within the 15 minutes it took to get him home, poor old Travis started vomiting and having diarrhead. Once all the stool was cleared out of his system, he produced several movements that were only worms. A lot of worms. It was like something out of a horror movie. It didn't work on the mange, but at least that was the last time he ever had worms of any kind. The heartworm preventive took care of any possible future infestations.
Untreated worm infections can eventually kill a dog because the dog doesn't get enough nutrients. Same thing with flea infestations. Get enough fleas on a dog for a long enough period and the dog will get dangerously anemic and eventually die. When over the counter remedies don't work (and OTC wormers don't hit many kinds of worms) you need professional help. :-)