Endometrial Biopsy

We had our first appointment with a fertility specialist on Tuesday. He outlined his plan for us, which started with bloodwork and an ultrasound in his office followed by more tests that are all part of the fertility workup. They got my blood test results today and want me to come in tomorrow for an endometrial biopsy. I am 2 weeks late for my period and thought he wanted me to start provera first and then my testing would begin on cd3. Anyone know why they’re having me come in for the biopsy so soon? Any advice? I’m a little nervous, I’ve read a lot of comments saying it’s painful.