Is the dewormer working?

A few weeks ago I found a stray kitten. Starving and with a bad respiratory infection. He had a pot belly which I guessed was due to worms as I've had cats in the past with them. He was eating, drinking and going to the bathroom well. It all looked normal. Took a stool sample to the vet they said he did have some. So they prescribed Pyrantel Pamoate, 3 doses, 1 every ten days. Didn't notice anything remarkable in his stool. Just tiny white flecks. Are those parasites? Then I took him to a more affordable veterinarian for his respiratory infection. He said he was still full of worms as well and acted somewhat surprised that the previous vet only had him taking it every ten days. So he gave me 3 doses of the same medication to be given for three consecutive days and then continue with the first vet's schedule ten days later. Now the kitten has diareaha and I still only see white flecks in his stool. He is on medication, Clavamox, for his uri as well. Still has a pot belly. But he eats, drinks, plays, urinates and poops normally (except for the diarreah). Acts like a mischevious little boy cat.
Are those flecks eggs or grown parasites in his poop? Is the medicine working? His belly is still huge.

Some kittens just have a pot bellies. It looks like he is doing fine so the medicine has to be working otherwise he would be really sick. I had a kitten full of roundworms and she almost died because of it. She was very very sick when I found her and she was full of them. That doesn't seem to be what is going on with your kitten so the medicine must be working. I would let the vet know what is going on and what you see in his feces and see if the vet is concerned.