Sandi, my Pixie became very ill with vomit and loose bowels. The vet did many tests and couldn't come up with an answer. After each trip to the vet she would feel better for awhile, and then the problem would start again. Pixie kept getting dehydrated too, was lethargic and generally miserable. One day I spotted some tape worm eggs and called the vet. She gave me one Cestex pill that works on tapeworm. After 2 days Pixie was cured, it was like a miracle, because I really thought I was going to lose her. The tapeworm is not always found in fecal tests, and some cats are very very sensitive to the tapeworm.
Just wanted to share this info because her illness was so mysterious, the vet was totally stumped by her blood test results.