Since your dog has already been to many vets I may not have much to add so please forgive any repetition.
If your dog is smelling her perianal area she may have some flatulence that she may find offensive either because it smells bad or because it may burn or cause pain when the gas comes out. You might try a probiotic, digestive enzymes, and Beano anti-gas formula, and/or Gas-X for this problem. Most dogs (and cats and humans) should be on a good probiotic anyway. VSL-3 is a probiotic available online (amazon.com) that is recommended by many veterinary nutritionists.
A human pediatric digestive enzyme is safe and may also help.
Beano and Gas-X are available in markets and drug stores and can help to eliminate flatulence.
A grain-free hypo-allergenic diet may help.
One of the Chinese herbal formula's: Stomach Happy, Happy Earth, or Jade Lady may help also. These formulas help with a Chinese diagnosis called Spleen Qi deficiencies which are issues with digestion. These are available by prescription from your veterinarian from the Jing Tang Herbal Company.
A visit with a veterinary acupuncturist may also help, as could a course of steroids for perianal inflammation.
Another possibility is that there may be pain in the gastrointestinal system. If pain medication has not been tried than perhaps Rimadyl and Tramadol could be attempted as a therapeutic trial as long as she is not taking steroids.
Lastly, it may be a good idea to have an endoscopic exam or lower GI (colonoscopy) with biopsy.
IVDD? (Intervertabral Disc Disease)...I'd check for this.....Karla
P.S. I'm hoping the Vet will pop in soon to answer your question.....
My dog does the same thing. She is a spayed fem lab/shepherd, age 5. She has reoccurring bouts of cystitis. Blood work is normal but her bladder spasms. She gets up and runs, spins in circles and drags her butt on the floor. My vet put her on 2 pills a day of Proin Tab 50 mg 2x daily. She does not leak urine anymore and it stops the pain in her bladder. maybe your dog is suffering from the same thing. It may be worth a try. They also have a fish antibiotic called fish Mox forte, Its for ick....If you type the medication into your puter the tell you how its used for dogs that have bladder spasams. They get a bacterial infection(allergy) from water, grass, and dirt. these tabs are cheaper and cure the pet. I have given it to Annie and it works like a charm.Perhaps you might want to look it up and see if its something you want to try.
Brooke