pills to make period come

I have been having trouble getting my period since last AUG. I went to gyno today she told me everything looked normal (had some sort of ultrasound thing done). Not preg. Thinks it's endocrine system. She gave me some pills to take for 3 days (choice between pills or shot in the bum) should induce period in 1 week. It's not birth control pills. has anyone heard of this scenario? SHE said that every three months if I don't get a period to go in and take pills or shot so i don't get problems/abnormalities with endometrium or uteris.