First off Welcome ! I have been away for a bit and have missed many newbies.
There are SO MANY conditions that can cause this. It is a process of elimination and SLOW changes.
Everyone here has an opinion. Some might even be vets or techs. But each dog is different. So take EACH post, comment and opinion slowly.
There are many common and general conditions related to food and environment.
Elsewhere on this site is a list of dog food ratings. Just because something is a 5,6 7 star does NOT mean that is what you need to have. Each dog is different.
But stay away from the 1,2,3 items. If you change dog food brands, swtich slowly. MANY Bullies are allergic to chicken and grain products. Not all.
Ues metal bowls, plastic can cause irritations.
Your vet can either do a allergen testing or can refer to a specialist. Use, just like people, they are allergic to lots of things.
Don't stress, take small steps. Keep posting, read replies.