I am sorry your kitty is having so much trouble.
How old is he exactly?
Is he neutered?
Recently vaccinated (within last few weeks)?
Does he go outside?
Did your vet run any blood tests or take any x-rays?
Did your vet put him on any meds?
Has he been tested for feline aids and leukemia? Has he been dewormed?
Let me know and i will try to help.....
Thanks for the additional information. I am pretty worried about your kitty, and want you to take him back to the vet immediately. It is VERY dangerous for a kitty to go too long without being able to eat, and as long as your kitty is vomiting, he cannot take anything in orally. In addition to not eating, he is not passing urine or feces, and this is dangerous as well. Kidneys and liver have very sprcific nutritional requirements, and ca start to shut down without adequate nutritional support. Cats in particular are prone to an illness called hepatic lilpidosis, which can occur if a kitty loses too much weight in a short period or if kitty doesn't eat enough. Please see the following website for more information on hepatic lipidosis.
Even though your kitty is currently playing and acting normally otherwise, this will not last. The longer he is not able to eat, defecate or urinate, the more dehydrated and decompensated he will become. It will save you alot of money and your kitty alot of discomfort and complications if you have him seen ASAP.
Possible causes of the symptoms you are seeing include things like pancreatitis, which can occur if kitty ingested some people food or garbage. This illness is life threatening and typically requires hospitalization and iv fluids to treat. An ultrasound is more helpful than x-rays to diagnose pancreatitis. Another possibility is that your kitty swallowed a foreign object and is experiencing an obstruction. Even though your vet took some radiographs, this is still possible as sometimes a series of films is necessary to identify this problem.
Your kitty needs an exam, some bloodwork and some more radiographs, and maybe an ultrasound. Please try to have him seen ASAP so that he can feel better. Please let me know if I can be of further assistance. If this has been helpful, please hit the green accept button. Good luck!