How is an anal fissure self-diagnosed?

With a mirror? Could you be referring to fissures, fistula, abscess? Sexually transmitted disease (syphilis, gc, hiv, etc.) should be considered. Hemorrhoids & rectal prolapse can appear as an outward bulging. Anal trauma of any kind may cause mechanical injury. Skin eruptions need to be considered. Evaluation is recommended to distinguish serious versus less concerning reasons for your problem as described.