Sounds like they are treating the cat for what they don't know what's wrong with em...

So u wasted ur money going to get that done... so it's either there was nothing wrong with your cat or if there is something wrong the vet did not figure it out

Curious if its a long haired cat? My cat had really long hair and it was thick, he would do this from time to time before hacking up a hairball. His appetite would be less during these periods too.
(He was even on an indoor/weight/hairball food)
However i would hate for this to be something else for your cat and more severe.