Hello,
Well it sounds like you are addressing many of the usual suspects. I would say at this point that you call your vet back and tell them what’s going on. If you were my client I would recommend a recheck to include a rectal exam for anal sacs (some refill in a matter of weeks) a rectal exam of the colon (for masses or abnormalities causing discomfort), a thorough check for fleas (and to make sure Parasiticides are being given appropriately), and a talk about allergies with better medication options given to help eradicate the itch. This is where I would start. Yo it dog is either uncomfortable or itchy. Check again and try to rule out one versus the other. Also if they are scoring to the point of trauma to the skin you may need an antibiotic or topical treatment for the skin in the urogenital/rectal area. Let me know what happens. Good luck.
The forum says there is a response on my question but it isn’t popping up. Can you please repost it?