Maxie, get back to the vet, ask them to do a blood test for kidney function, don't waste any time. My cat Rover was just like this two years ago - wasting away, sad, throwing up all his food. The vet was going to do an exploratory op thinking it was a blockage but when they did the pre-op blood tests, it came up straight away that his kidneys were failing. Apparently with cats, the damage has to be pretty bad (up to 75% damage) before the symptoms start to show - his stomach was full of bile making him so sick all the time. Anyway they kept him in for two days rehydrating him, then started him on Fortekor tablets one a day, and I am happy to say that two years later - about about 13 years old - he is full of beans and back to his normal bouncy self. He has to have a tablet every day but they have a tasty coating which he loves, he asks for his tablet before breakfast every day. Please get your vet to do this test - or change your vet and get a second opinion. Poor old Rover was ravenous and thirsty and going downhill fast two years ago, but his condition meant that nothing was staying in. Kidney problems are apparently very common in older cats (and I lost two cats to kidney failure 30 years ago), but these days there is treatment and we are looking forward to a good few years with him yet. Good luck to you and your cat - let us know how you get on!