HELP my 17 year old cat!

I have a 17 year old cat, who until recently has been very fit and active, so much so that nobody believes that he is 17. Over the Christmas period I have noticed that my little man is constantly hungry, so I feed him, he has always been a slim cat, but now he is losing so much weight. During the night he sleeps in the bathroom and for the past week he has left behind something in the bath, I know this is rather unpleasent but I am not sure if it is poo or vomit, as it looks like a mixture of both, and smells as bad! I would be devestated if anything was to happen to him as he is such an imprtant member of our family. If there is anyone who could help or has had a similar experience then please, please, please leave me some advice. Thsnk you

he could also be diabetic or have feleuk. he needs to have a complete blood panal done & be tested for feleuk, & FIV

i agree that you need to get your kitty to a vet asap please. there is a chance your kitty is in pain so while you have the vet run tests i'm sure you will want to get pain meds or whatever kind of meds for kitty so he is not in pain. if you have any doubts as to what the problem is please bring kitty for a second opinion to another vet place. good luck. sending you many get well vibes for your kitty.