Thanks for posting your query.
Fistula in any part of body requires debridement and correction of basic pathology.
Fistula in ano may develop due to ischio-rectal abscess
, inflammatory bowel disease
You should consult with surgeon and should get thorough check up.
Primary pathology must be treated for permanent cure.
Laxative will help in decreasing pain but never treat disease permanently.
Dr. Mayank Bhargava