haven't had a period in 4 motnhs?

Ivycan

I've lost a stone since June and since then my periods have stopped. I now weigh 7 stone 7 pounds at 5ft 3, i'm 19 and i don't do any strenuous exercise (i know i should) I've been to the doctors, blood test normal, just got told i'm iron deficient, and now am being referred for ultrasound. I'm really worried as to why its stopped and can't help but think it's something to do with my diet, but my doctor hasn't weighed me nor commented on my diet atall

Has anyone else experienced this?