Any surgery that we do on the anus, haemorrhoid (piles), fistula or fissure treatment, that leaves an open wound on the anus, will come with increased pain after surgery. That usually lasts for 7-10 days. It is most intense after opening your bowel. For the same reason it is advised you take your painkillers half an hour before planning to go to the toilet.
There is usually a haemostatic sponge left in the Anus that will fall out either spontaneously or with the first bowel movement. It is not painful when it happens.
It is also best if you keep cleaning the Anus with water at least 3 times a day, including after every bowel movement. Use minimal amount of toilet paper. The most ideal tool is a bidet but in the lack of that (not many houses have one) you can use sitz bath, or the shower either in the shower cabin or by sitting on the edge of the bath tub. A few days later you can start using gentle soap or shower gel.
Keep taking the painkillers as needed, the Antibiotics (Metronidazole) and the laxatives (Lactulose or Movicol) to avoid constipation that can happen simply because of the fear of pain during defecation. Constipation will lead to a larger, harder stool eventually that will hurt more.
You do not need to use any special dressing. You can keep a simple pad in the underwear for protection. Not protecting the wound, but the underwear. The initially blood stained mucusy discharge will clear up slow down significantly in the first week.