My bulldog was going through the same thing. Had the skin scraping which turned out negative. Vet seems to think allergies. He had an allergy shot. I did not change his diet in anyway but I do suspect it might be a grass allergy. So I always wash his feet after going outdoors and spray them with a spray made of alcohol and salted water but only if I see him chewing his feet. I bathe him as needed and always wipe his underside and face when he's been out. Eventually the hair he lost on his back grew back. My other female bulldog has displayed some welts on one side of her flank and the fur fell out there but I am hoping it will grow back. Other than that she does not exhibit any signs of distress and the welts disappeared. Any of the allergy meds given to my male bulldog does not seem to any effect on his allergy symptoms. I'm very aware of the distress this can cause to the caring owner. All I can say is hang in there. In my case the fur did grow back. It's a learning experience being the owner of a bulldog and hopefully whatever we learn from our experiences we can pass on to others on websites like this.