What Is The Pus Filled Boil In Spite Of Taking Medication?

My husband (33) has a boil on his chin. He went to the ER on Saturday and they prescribed Bactrim. They did not lance the boil since it had already ruptured.. After 3 full days on this antibiotic, there is still pus draining and the boil does not seem to be improving. He is concerned because a little less than a year ago, he also had a boil accompanied by MRSA. He is wondering if he needs to return to the doctor or give it a few more days.