Just this last week, I took my 12 year old tortie, Kitty, to the vet. She has a good appetite but was vomiting a lot and had lost weight. Other than the vomiting, she seemed fine, and in fact still plays like a kitten. Her blood work looked great. The vet suggested an x-ray. The x-ray showed a mass in her abdomen. I was then referred to a specialist for an ultrasound. We went yesterday for that and it was determined that Kitty has a mass in her small intestine and an inflamed lymphnode adjacent to the mass. The vet expected it to be lymphoma but a needle biopsy revealed the mass to be mast cell cancer.
I have read that common signs of problems like this can be loss of appetite and weight loss. Hopefully, your kitty is not as sick as mine but the x-ray and/or ultrasound is probably worth doing if you can afford it. Of course, you may want to get thyroid checked first as ultrasounds are expensive.
Good luck to you and your kitty!