I'm not a doctor, but it isn't uncommon for fecal matter to irritate skin.

If the bumps are surrounding the ****, I would say that the acidity of the feces is the cause of skin irritation. If, however, the bumps are on your buttock muscles, the rash is probably caused by something else.

Be sure to wash the area gently with a mild soap. Don't use harsh temperatures or scented soaps. Those two are biggies for taking good care of skin ~ sensitivity waxes and wanes throughout our lives. Unscented soaps helps a lot as does tepid water temperature. If that doesn't help at all, see a doctor.

That's my advice ~ hope that things improve for you soon!