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There are a few possibilities for what may be going on with your cat, but at the top of my list is my concern that he may have FLUTD (feline lower urinary tract disease), also called FUS (feline urological syndrome).
With this problem, crystals can form in the urine. These crystals can precipitate out of the urine solution and form little stones in the bladder. It hurts to pass them! So, when the cat urinates, it stings.
Unfortunately, with male cats this can also quickly progress to a life threatening emergency if one of the stones plugs the urethra (the tube from the bladder out the penis). Suddenly, you can have a cat who can only pee tiny amounts or not at all. Without immediate treatment, this can be fatal in within 24 hours!
If the cat is unable to urinate, then the toxins the kidneys are meant to be clearing can build up in the blood stream. These make the cat feel nauseated, and can make him vomit, lose his appetite and become very lethargic as they build up.
If your cat came in to see me at my clinic, I would check his bladder to see if it was hard and painful, or not. I would make sure he could urinate (by passing a catheter if he was obstructed) and take a sample of the urine to determine what type of crystals were present. Then, I would start him on a prescription food to dissolve those crystals. I would also start him on antibiotics if he needed them.
Many cats need to have a urinary catheter kept in place if they are blocked so that the bladder can be completey emptied and flushed to remove crystals.
So, in summary, I think your boy is trying to tell you that he has abdominal discomfort. This could be due to pancreatitis, gastroenteritis, or urinary obstruction. You need to get him to a veterinarian promptly - today!
THIS IS AN EMERGENCY!
I'll give you some links to further information. I do urge you to seek veterinary care promptly before this becomes more complicated (and painful and expensive). I truly don't think this is going to get better on its own!
If you feel this has answered your question, please hit the green Accept button. I will still be here to provide more information if you need it.
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.
Please let me know how he does!