[Lillith]

Have you had him evaluated by a vet? Did they check his thyroid, do any other blood tests? Some medical issues, such as the thyroid, can cause a sudden change in behavior.

 

[Lillith]

I haven't had him checked for his thyroid or any bloods, i have been to the vet multiple times during all of this and not once have they suggested it be someone health related. He is due for his annual checkup soon so will speak to them about this then.

With training, i probably am somewhat lenient i.e. letting him jump on the couch once in a while within permission but that's about it.

Vet's don't always know the entire history of your dog. They may not realize how quickly this behavior change took place, and they may not think to test for certain illnesses if the dog isn't displaying certain symptoms. It never hurts to ask for them to perform those tests, though.