Simone is a 22 year old pharmacist who is seen in the Gynaecology clinic with a 6 month history of pelvic pain. She has a 28 day menstrual cycle but periods are very painful and she also complains of deep dyspareunia. She has been trying to conceive with her partner now for 9 months. This is her first sexual partner and a recent STI screen returned negative.
What is the most likely diagnosis?