If since several weeks or months pain occurrs, sometimes more, sometimes less, the reason could be a so-called chronic anal fissure - a small ulcer that can be felt by oneself, mostly on the back, on women often on the front end of the after as well.
The margins are rough and often there is a rough skin proliferation or a little skin flap on the outer margin, the so-called marisca. On the inner end of the fissure the examiner often sees a small anal polyp. Those two signs show unerringly that the fissure already exists for some time.
Not only pain indicates a chronic anal fissure, there can also be itching or an eczema due to constant weeping of the open wound, and of course there can be blood on the feces or the toilet paper.