A 5-month-old boy is brought to an outpatient pediatric clinic by his parents due to a week of increasingly poor feeding and mild irritability. He recently completed a 10-day course of oral amoxicillin-clavulanate for a suspected acute otitis media. His parents report no fever, vomiting, or diarrhea. On physical examination, the infant is afebrile with stable vital signs. Examination of the oral cavity reveals creamy white plaques on the tongue and buccal mucosa which can be partially scraped off. There is no associated erythema or ulceration of the surrounding mucosa. Which of the following is the most likely diagnosis for this patient's condition and the initial step in her management?