Since you have a male I would say that possibly he has urine crystals blocking his urethra and is full of urine. Kidneys will fail. I am not a vet and only going by what you have said... but I have seen this happen first hand with a cat I had but he had to be put to sleep because I didn't know any better. This was in 2004 and was the most horrible thing I ever witnessed.
As LavenderRott, he's dying a slow and painful death. His moans will get louder and louder and he
will suffer.
If he's got the crystal blockage, a final vet visit is your only option if you don't have the money for surgery (of which there is no guarantee anyway). There are no home remedy fixes for your kitty's problem.