A previously healthy, afebrile 7-year-old male who has just returned from his spring break in Florida presents with this swollen red area behind his right ear. His tympanic membranes are normal, but the moderately painful swollen ear canal has some whitish debris. After his visit to the emergency department 2 days ago, he was prescribed high-dose amoxicillin and topical antibiotics for his earache. His mother cannot remember the name of the drops. Why has his condition worsened in the past 24 hours?