Hi I am a 12 year old girl, thirteen soon. I am quite slim and weigh around 6 st 10 lb and am 5 ft 1 in. When I wake up my stomach is completely flat, but before I go to bed I swear I look pregnant and I don't know why. I walk 30 miles a week and have a healthy balanced diet. Is this normal? Do I need to work up my stomach muscles to hold it in a bit more? I'm really desperate because my friends do not have this problem so I need advice!!!