What can I do about the large hole in the back of my ear piercing?

Apply Plato's Scar Serum on the scar and allow it to close without placing the earring back in. Later, you can repierce. Best, Dr. KaramanoukianLos Angeles

Your description of the ear piercing wound suggests the retainer was pushing into the back of the ear, and this created a pressure wound on this surface.  If you want to maintain the piercing, I suggest you keep the post in place with a much looser position of the retainer backing.  You may use a piece of cotton over the wound (around the post) to keep it from macerating.  Unless the ear becomes very red and painful, the wound should heal in a week or two with concentric contraction of the edges.  If you suspect any infection, seek the evaluation of your physician.  

From your description, it sounds as though the back of the earlobe is wounded and this is most likely from the earring backing/retainer.  The risk is that if there is infection there, keeping the earring in place would not be recommended.  If no infection, then possibly allowing the wound to heal with the earring in place could work.  Consider a consultation with a Board Certified Plastic Surgeon and best wishes to you.Garrett A. Wirth, MD, MS, FACS
Wirth Plastic Surgery
Wirthplasticsurgery.com