This happened to our cat a few years ago. Turns out he had eaten some thread. Part of it was wrapped around the back of his tongue while the rest was making its way thru his digestive tract. Regardless of what's ailing your cat, get him in to the vet ASAP. Good luck!
How old is your cat? Sometimes there just old. It might be the enzymes are not working well and he can't digest properly. About the meow it could be a throat infection, can't meow or eat. Take him the Vet, they know what to do.