A 22-year-old female patient complains of dull pain in her right iliac area that she has been experiencing for a week, morning sickness and gustatory change. She has a history of menstruation delay for 3 weeks. Objectively: AP-80/50 mm Hg, pulse is 78 bpm, body temperature is 37°C. Bimanual examination reveals that uterus is enlarged, soft, mobile and painless. Uterine appendages are palpable on the right, there is a dense, elastic and moderately painful formation 3x4 cm large. What is the most likely diagnosis?