Dogs do lots of things when they are anxious but I'm not sure I've ever heard of scratching themselves. Particularly with the bulldog's sensitive skin, I would definitely see whether or not you can get to the bottom of some kind allergic reaction that might be going on. The other thing could be an ear infection, which is super common and not always detectable until you go see the vet. I would take a peek in his ears to see if they are dirty, smelly, red, or otherwise inflamed. Does the area he's scratching look dry, inflamed, or upset? The spots might not be mange but it could be a fungal infection, which isn't a test most vets perform (and it's expensive) but it could be that too - but from what you say between the rubbing the head on the floor and the itching the ear and neck area, it really sounds like an ear infection to me.