<s>[INST] My partner has developed a solid lump about 2cm on the INSIDE of his left buttock close to his anal passage.  He's in absolute agony with it. What could it be?  This is the fourth day he's had it now and it's just gotten more painful.  He does a lot of driving, could this be the reason why? [/INST] Hi,From history it seems that there might be having developing abscess over that region.This can be due to ingrown hair follicle infection and part remained more wet due to perspiration and less airy.Her might require one course of antibiotic and anti-inflammatory medicine course for 5 days.Once abscess is formed, it might require incision and drainage of pus.With antibiotic medicine there are all chances of clearing the infection.Ok and take care. </s>