My older cat Ash also has a problem with throwing up, he can go ages without doing it, and then has a few weeks where he just throws up after every meal, we go through lots of carpet spray in my house, my vet does not seem overly concerned, as Ash has not lost any weight,infact he has probably put on some, and is a rather large boy, but i still worry about it, and hope its nothing more sinister, he was a stray ,so who knows what rubbish he ate before that. hope you get to the bottom of the problem, i know how fustrating it can be.