Steroids have their place to be sure. But, sometimes in my opinion exacerbate and or create other problems. Such as slow healing wounds surgical or otherwise.
GD does not usually involve the face. In my case it was total body save and except the soles of my feet, arm pits, groin and my face. Strange really when considered. Much of the literature indicates the predisposition of GD has to do with sweat and moist skin areas. They guess, and we have a word for it, "Idiopathic". I remember it this way, Idiopathic, means Idiots just don't know.
You need a biopsy. The Biopsy required is what is termed a punch biopsy but relatively painless. A local anesthetic will be administered first. Suggest an area that is accessible to you. Its hard to clean and dress the wound it will produce when it is on your back. But that's just me. I don't want to trouble others.
You and your Dermatologist need a definitive diagnosis to treat effectively. I have never been a fan of the shotgun method. Lets appropriately diagnose and treat the pathologically diagnosed problem. There is a joke in the medical community regarding Dermatology. It goes like this, "If its wet make it dry if its dry make it wet".
Lets practice real medicine