Caitlin is a 16-year-old cis-gender female referred by her pediatrician for six months of amenorrhea.  She says that her menses were once a month until about a year ago. At that time, she missed two months of menses, had one bleeding episode that was very light and only lasted three days, and then had one day of spotting a few months later. She has had no bleeding for six months.  When she previously had monthly periods, they generally lasted 4-5 days. She used pads and changed them every four hours.   She is in 10^th grade, plays basketball in the winter, and runs track in the fall and the spring.  She runs about 3 miles five days a week with strength training in between.  She has never had a stress fracture.  Her mother is with her at the appointment and tells you that Caitlin has lost about five pounds this year and has been very focused on making healthy eating choices since she started high school. When interviewed alone, she denies any current or previous sexual activity.