A good physical should reveal the answer, but if the irritation is substantial, then heavy sedation may be required to minimize patient discomfort.
Frequently an anal sac abscess or perforation is found to have caused the inordinate attention. Treatment is straight forward. Rectal pruritus (itching) may be a minor source of this problem, and there can be a number of causes, such as allergies, intestinal parasitism, ecto-parasites such as fleas/mites, contact dermatitis, etc.
Have a visit with your favorite veterinarian and get to the bottom of this problem.
Dr. Van Lienden
Dr. Raymond Van Lienden DVM
The Animal Clinic of Clifton
12702 Chapel Road, Clifton
Virginia, U.S.A. 20124