About a month ago my 2 year old female pug (she's spayed) started chewing at her vulva. I examined it and it was discolored and looked like it had a lesion on it towards the inside of it. It also had a couple spots that looked like they were pustuals. We took her to the vet. They did a UA and found nothing unusual. They really didn't know what was going on so they gave her antibiotics and put her on prednisolone for the itching and inflamation. That seemed to help even though her vulva never really looked normal after that. A couple days ago she started licking and knawing at it again. I examined it again and it looks horrible. It looks scabbed over. Some of it is red and some of it is white. She's a black dog so it's usually black. She's started dragging her hind end across the carpet for relief. Have you ever heard of anything like this? I don't know how to help her.
It's possible that she has vaginitis which is causing the itching, and the antibiotics and prednisolone only worked for so long, or she could have a yeast infection which needs an anti-fungal medication, so, the antibiotics didn't do the trick.
The following webpage examines vaginal discharge and also discusses unspayed dogs, but in addition it does contain some information relevant to her symptoms, so I thought it might be helpful:
I'd have her re-evaluated at this time and try to get to the bottom of the problem. Is she urinating normally? Does she ever get UTI's? If she's prone to urinary infections, this might be a related symptom. I realize her last urinalysis was fine, but you can never tell what's happening at this time, a month later. She may be constantly irritated by her own urine, so try cleaning her with something like MalAcetic Wet Wipes/Dry Bath in that area. Look for it, or something similar, in pet supply stores.
It's also possible that something she's coming in contact with when she urinates/defecates or just sits, is causing an allergic reaction.
I hope you and your vet will be able to alleviate her discomfort very soon and I wish you good luck!
Extensive Experience Caring for Canines; Specializing in behavior and health concerns.