A 17-year-old male presents with a complaint of recurrent nosebleeds. He reports that in the past his nosebleeds have continued for hours despite digital pressure. He also reports that his gums bleed easily, and he bruises easily. Blood work reveals a WBC count of 9,000/microliter, hemoglobin 10 grams/dL, platelets 95,000/microliter, PT 11, PTT 32, and INR 1.3. The bleeding time is prolonged, and his platelets appear not to aggregate. He denies the use of any medications. What is the most likely diagnosis?