What Could Be The Cause For Irregular Periods And Hair Fall Problem?

Question : My daughter is 17. She got her first period at 13. She was never a heavy girl but decided 18 months ago to be a healthy girl. She eats lean proteins and lots of vegetables. She eats a well balanced diet. I wish she would eat a little more red meat. Her iron levels are borderline normal. But within the normal range. They have done some blood work and say it is all normal. She has not had a period in over a year. She weighed 118 pounds when she had her last period and now she is 108. She is 5'4" tall. She is a cross country runner. She was blessed with a XXXXXXX of gorgeous hair which is over half gone at this point. I am getting no answers just that she needs to gain weight and dramatically reduce any exercise. A lot of advice I cannot accept because I was the same as her when I was young with the exception that I did not eat healthy. I was thin. They want her to take birth control pills but I feel there is something more to this. The hair disappeared in July and that was a year after any diet changes to the lean and healthy one. Do you have any thoughts on this or I am just spinning my wheels. The nurse practitioner at the OB office feels I am correct and there is more to this but her hands are ties as far as going any further. The endocrine doctor was not helpful. Nor was the dermatologist. OH, and she is also constipated so when it was said to take an iron pill, I hesitated. We just added more to her diet that was rich in iron. A lot of cereals have iron and we were cooking in a cast iron skillet. We have not had iron checked again but there have been no changes to the hair.

I am not sure about all of the tests. They are checking male hormone levels now. She is a typical high school student with tests and everyday issues. The thing is that she lost hair during the summer which I know could be from previous stress but there is no sign of anything growing back. She doesn't feel overly stressed. She takes a multivitamin already and extra biotin. I am worried about iron because she is constipated. She did have ultrasound and ovaries looked normal. But something is still not right. As I told the doctors we have seen, the period stopped before there were any lifestyle changes. The other thing she feels is that she eats the way she does because if she eats sugar or snacks or other foods, her weight jumps up considerably. She really fights as a young person to be comfortable. She is not shockingly thin either. She really looks normal. But as I mentioned she struggles to be thin.