I am 21 and 5"5. 6 months ago I weighed 13st 1, without any change to my routine or diet I now weigh 11st 4. I was always a size 14 but now I am a small size 14/12. Yes, I am happy to have lost weight but concerned as it was unintentional and I feel continuously tired and fatigued. My gp thinks me losing weight is great but I'm concerned.