Yellow seed-like things from my kitten's?

Hi, I'm raising a male kitten who is 3~4 months old now. Since he came to my home, I can find some yellow seed-like things. It looks like some sesames on the hamberger buns but yellow. These can be found where the cat has stayed/slept for many hours. So I researched in the internet and many ppl were saying that it can be a segment of tapeworms. So I took the yellow things to the vet. hospital. The doctors looked those through the microscopes n thery were saying it can't be animal things b/c the kitten already has done revolution, n he ate meds to deworm for twice. But today, when I was holding the kitten I saw a white small seed-like worm coming out of his . I took that to the hospital(took only 20 mins) n the small worm became yellow and hard just like a sesame on the hamberger buns. The doctors don't know what to do, n we already tested his poop n nothing came out. He doesn't have n e bleeding, no diarrhia and no symtoms. What can I do? Does n e one know what these yellow things are?