A 28-year old woman presents with several painful ulcers she has developed in the vaginal area. Examination reveals multiple 0.5 cm to 1.5 cm oval ulcers with sharply defined borders and a yellowish-white membrane. She denies recent sexual activity. Except for recurring aphthous ulcers of her mouth, her past history is unremarkable. At this time, which of the following is the most likely diagnosis?
