U are suffering from fissure in ano....fissure is a wound in anal opening which is caused due to constipation.
whenever motion touches this fissure( wound) it cause pain and burning sensation
If you want to know more you can consult me online
Next Steps
take a laxative syrup to get liquid motion( for relief of constipation)
apply local anaesthetic gel before going to motion and after
take a pain reliefing tablet two times a day
Health Tips
take hot sitz bath( sitting in warm water for 15 mins for 2 times a day
avoid spicy food
high fibre diet
drink plenty of fluid