Thanks for the query to H.C.M. Forum.
Almost 24 years passes after anoplasty , so this , may not be a cause.
As far as concerned about burning sensation and pain in rectum
may be due to some pathology in rectal area ( colon, anus, rectum). Colonoscopy
may find out some reason.
In my opinion vaginal culture will not find any disease.
History of sexual contact is very important in this case.