What wolfy dog said.
Had there been a fairly recent rabies vaccine given within a couple of months of the change in behaviour?
What about HW/Flea prevention? Anything new? Oral, spot-on or collars?
Any other vet scripted treatments? NSAIDS, Steroids?
Could just be spring. In TCM, spring is the season of anger. Liver detox - Milk thistle
He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion. - Unknown