Maya is 20 years old and presents to A&E with a 1 day history of right sided lower abdominal pain and nausea. She denies any urinary symptoms, vaginal bleeding or any fevers. She is sexually active and her recent STI screen was normal. Her menstrual cycle is irregular and occurs every 4 – 7 weeks. She insists good compliance with the combined hormonal oral contraceptive pill and her last menstrual period was 6 weeks ago.
On examination, her abdomen is tender on palpation of the right iliac fossa with some guarding. Observations are all stable.
What is the most likely diagnosis?