10 yr. old Lab losing weight and vomiting

Question
Hi - I have a yellow lab who will be turning 10 in December.  About 2 months ago, my wife and I noticed that he was EXTREMELY lethargic one day and could barely get around.  He also would not eat a thing.  Obviously, I rushed him to the vet who gave me a bottle of 500mg Cipro as he thought it was merely a bug that might have been picked up.  He took blood work that showed to be okay except he did say his liver enzymes were elevated but not too severely.  Four days ago my wife fed the dogs but he ate less than half of his food which is very uncharacteristic.  She said he went back to the bathroom and laid on the tile and once again, had a very sick lethargic look about him.  This time though he vomited all over the bathroom.  Shortly after this my wife had to run an errand and left the dog in the house because she felt bad about leaving and putting him back outside.  When she returned there was vomit all over the house.  I was out of town at the time but when I returned I noticed that he looked extremely thin through the stomach.  His energy level however seems to be normal now but he doesn't seem to be putting any weight back on.  

Some other things to consider:
1) Everytime we take the three dogs to the park or walking on the leash after they've eaten he vomits - Everytime!
2) He urinates like a never-ending water faucet
3) He recently developed a "benign fatty tumor" according to the vet on his front leg about the size of a silver dollar.  It doesn't pain him at all when it's touched.

Could this be Diabetes? Cancer? thyroid issue?

I would really appreciate any advice or opinions.  I'm worried about him...

Answer
Hello Chris, I am so sorry for your worries, I know how bad it can be.  I would be suspicious of Kidney failure.  These symptoms are similar.  Even if the blood test did not show signs of this before, I would have them repeated.  There is something going on and not to much can be diagnosed without current blood test.  He might even need a special dog food such as KD or LD, one specific for the liver or kidneys.  Please go back to the vet and have the blood redone.  Good Luck and I hope things do get better.  Thanks for asking, Cindy Lou :)