My dog is shaking, excessive drinking/peeing concentrated dark yellow, lost weight, eats well, can anyone help?

The urinalysis shows that the urine is not diluted, so the vet says no kidney/bladder disease. There's slight elevation of 2 liver enzymes (alt, ast). Blood tests came out normal. The only other abnormality is the orangish color of the urine which often indicates liver disease. But usually liver disease involves vomiting/diarrhea - none of which applies. No jaundice. The vet says that it couldn't be Cushings disease or a brain tumor because then the urine would be dilluted. My dog drinks at least 2 1/2 cups of water a day. I'm so frustrated to see my beautiful female English Pointer suffering from tremors, weakness, etc. She's only 8 years old, and has never had accidents in the house until recently. Also, sometimes she has trouble trying to sit down. Thanks for any help....