My 14 yr old Chocolate Lab displayed the same type of symptoms. Unfortunately, when I brought her to the vet she was diagnosed with bone cancer. They gave me meds, but at her age, she was pretty far gone. Had to have her put down as I just couldn't bear to see her suffer any longer. She was a great companion for all those years, and having to put her down was dam near the hardest thing I ever had to do. They say you know when and if you go to heaven, all the dogs you ever loved will be there to greet you.
Hopefully your situation is not like mine. Best of luck with you best friend.