Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
This does appear to be an allergic reaction that is causing so much irritation that he is also developing a pyoderma secondary to the irritation of the rubbing. The treatment of this is as follows:
Give Benadryl at 1 mg per pound every 12 hrs for 10 days.
Apply Betadine to the areas that appear red or irritated every 8 hrs. Clip away all the hair in this area. This is a skin infection called a pyoderma caused by the irritation. These can both be purchased at the pharmacy over the counter.
Bath weekly with Malaseb or Dermaplex which will remove the scabs or flakes. This can be purchased at the pet store or online.
You can also start the Macrolone and Enrofloxacin that was given prior because these medications will decrease the inflammation and kill the bacteria causing the infection causing the pyoderma causing pus. Either treatment will help your guy past this.
I ma so sorry that your dog is not feeling well. Unfortunately, due to my location, I am unable to make phone calls but I would lik to try to help.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, ***** *****