Best investigation endometriosis is :
Laparoscopy is the gold standard in the diagnosis of endometriosis. The diagnosis should be validated by peritoneal and tissue biopsy, because corpus luteal haematoma can resemble a chocolate cyst. Reference: Shaw's Textbook of Gynaecology 16th edition page no 415
Laparoscopy
USG
X-ray pelvis
CT Scan
Endometriosis and dysmenorrhea