It seems to be on and off, the vet said it was tape
worms based on the description I told them. I have gotten fecal tests several times and it always comes back negative, so when my cat poops there's nothing in the poop. But if it sits for a couple of days there are hundreds of little white worms squirming around in her feces.
I've tried the tapeworm medication 3 times, they always came back, im honestly not sure if they ever went away honestly.