Hi. I am really unsure what the "metallic" smell might be, although the rest of the symptoms sound to me like your dog has an infection. You should get him to see a vet straight away, and while you are waiting, please keep up the fluid intake. I am also concerned you have not altered the diet significantly over the last year - and you are feeding kibble, which is the worst food you can give a dog with kidney disease.
When were blood tests last undertaken and what were the results of those tests? Has your dog had a urinalysis undertaken? Has your vet performed a blood pressure check? When you say you are giving tripe and yoghurt - what kind of tripe are you feeding and what kind of yoghurt?
Tony