I would test this dog for a Tick Born Disease, Anaplasmosis (Ehrlichia equi) will cause those symptoms. I would run a CBC and Blood Chem also. Also Tick diseases seem to run in pairs.
A SNAP4 is cheap and will give you results in minutes, checks Heartworm, Lyme, Ehrlichia Canis and Anaplasmosis. This is a positive/negative test
Doxycycline is usually the drug of choice.