A 20-year-old female presents with increasing hair growth on her face and chest, deepening of her voice, and acne over the past year. She has no history of other medical problems. On examination, she has acne, abnormal male pattern balding, and enlargement of her clitoris. Blood tests show normal serum testosterone levels but a markedly elevated level of dihydroepiandrostenedione sulphate. What is the most likely diagnosis?