Hi, Welcome to Health care magic forum.
As you describe, it appears that the infection is very resistant, and may be a mixed infection.
You may need to have culture and sensitivity of the pus from the abscess
,and treatment accordingly.
The pain and blood at the time of passing stools may be due to the fissure in ano
, or piles, or may be due to the antibiotics, due to its irritant action.
I advise you to consult a surgeon for diagnosis and treatment.
Wishing for a quick and complete recovery. Thank you.