Hello, thank you for using this site to help you with your problem. My name is XXXXX XXXXX I have been in the dog field for 25 years. It will be my pleasure to help you today. Please understand that I may send an information request so that I may gather what I need to better help you with your problem.
Is it a sore near the anus?
Why is he on antibiotics?
No. I had an extra one from an ear infection he had earlier this year.
You are probably seeing an anal gland problem. Sometimes they get so full they blow a hole through the skin. I would have your vet give a look as soon as possible because it is painful and can quickly become infected
let me find you a site that talks more about this so you can get an understanding of what is happening
there is a picture in this link top left which shows what I am talking about
you are welcome. There are multiple pages to that link that tell you possible treatments needed including the removal of the glands, Just want to be sure you saw that
Is there anything else I can do for you today?