An<unk>  is an abscess (a large pocket of infection) adjacent to the anus.  The condition invariably becomes extremely painful, and usually worsens over the course of just a few days.  The pain may be limited and sporadic at first, but invariably worsens to a constant pain which can become very severe when body position is changed (e.g., when standing up, rolling over, and so forth).  Depending upon the exact location of the abscess, there can also be excruciating pain during bowel movements, though this is not always the case.  This condition may occur in isolation, but is frequently indicative of another underlying disorder, such as Crohn's disease.
Anal abscess
Anal fissure
Perianal abscess
Anal fistula
Anal cancer
Genital ulcer
Anal dysplasia
Fecaloma