Hi Judging from your symptoms the condition you have is called anal fissure. Like you said it happened after you passed larger feces. Also happens due to constipation excessively hard stools while passing cause a tearing of the anal skin. This injured area is has a rich nerve supply hence the pain everytime you pass stools. It would be helpful if you tell me the name of the ointment you are using. However if it is helping you can continue. But i would suggest you to go see a surgeon first as if this does not heal properly if can get infected and become complicated. Also please use some stool softeners like cremalax powder (contain fibres that soften stools)or syrups. Drink plenty of water as that is a natural remedy. Also please make sure you clean the anal area properly after defecating preferably with soap and water because if stool fragments remain in the fissure there is delayed healing and chance for infection. Hope this helps. Please take care.