Teenagers periods - stopped

[Egggywegggy]

Hi
Just looking to see if anyone has experienced this and can give advice

My dd (just 15) has been having regular periods for about 3 years

She has recently gone vegetarian and now goes to the Gym 3 times a week (for about 90 mins each time)

I know she doesn't have any type of eating disorder as she eats well, has daily vitamins etc and takes a healthy interest in her food, but she has lost some weight. (on 32nd centile BMI calculator)

Worryingly though her periods have ceased. I recorded a date on the calendar which was 5 weeks ago, and I am pretty sure she hasn't had a period for a couple of weeks before that.
(She isn't pregnant either!)

Is this normal? I've read that excessive exercise/weight loss can cause this, but I wouldn't put her in the excessive bracket

Just feeling a bit concerned before I take her off to the Dr

I'd go to the GP, aside from anything else she's still got hormones rampaging at that age and there may be a connection? But this happened to me (in my 30s) when I upped my exercise and changed my diet, so could well be that. After a bit of trial and error I discovered that if I'm under 60kg my periods stop. I'm still in the good BMI for my age and height if I'm under that, but for me 60kg seems to be my optimum weight (and if I'm honest, I did have a borderline eating disorder; it took a bit of work to keep under 60kg). Worth getting a doc's opinion.

Thanks - she is 5 ft 4 and weighs 50kg - I guess a trip to the Dr for a blood test would be a good idea, at least her hormones can be measured