Endometriosis??

For those who are familiar or have have Endo? How did you find out? What test were done?? They are whispering this to me and I have been checked out throughly before by a fertility doctor, does it just show up? Was blood work done, ultrasound?? I'm sad I thought I was pregnant but then when went to doctor I'm not and have some symptoms of Endo? I have an ultrasound for end of month? But I'm freaking out!