What Causes Brown Pus Discharge From Staph Wound Infection?

My 2 year old son has a staph infection on his butt, took him to the doctor about a week ago and they prescribed him an antibiotic and a topical cream. We haven t messed with it and let it drain on it own, today it opened and a large amount of brown pus continued to drain out. I m concerned on whether or not I should take him back to the hospital. Keep in mind, this is a very large area, the swelling covers half his butt cheek and feels like it s a pretty deep infection, and it s very painful for him.