How come i can't lose any weight?

I'm 15 1/2 year old girl and I have an extremely low metabolism, anything i eat sticks to me like glue, even if it is extremely healthy. For the past 3 months, all i've been eating is fruit + veggies for lunch/dinner and the tony ferguson sachets for brekkie + 6 dietary fibre capsules. I exercise every day for an hour. Even if i starve myself i can't seem to lose any weight. Why is this? And is there anything i can do to lose weight?