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I am sorry to hear you are worried about your cat. I am a veterinarian and will do my best to help.
Since he is on Vidalta, when was the last time blood tests were done to check his thyroid and kidney levels?
If he is not urinating, he is probably either dehydrated, and/or his kidneys may not be working. It is a good sign he is eating.
If you check his gums, are they pink or pale in color?
If I could, I would listen to his heart, take his blood pressure, feel his internal organs and lymph nodes, take his temperature (normal rectal temp is between 101 and 102; if he is over 103 he probably has a fever and if he is under 100 he is probably dehydrated). I would check for dehydration by gently pinching some skin over his shoulders and letting it go. The skin should go right back in less than one second; if it takes longer he is dehydrated and probably needs supplemental fluids.
How is your cat today?