I'm 14 and very thin :(?

I'm 14 years old and really skinny. I'm 5ft 4 and i weigh just 6 and a quater stone! :( my mum tells me all the time that its fine cos she was really skinny at school too. But i don't think she was as thin as me .. I havn't yet started my periods and my breats are small. I am a double A. :( I HATE MY BODY SO MUCH! :'( .. I eat so much i just don't understand! Even people that don't know m come up to me and put their hand around my wrist and say " you are so skinny".. it REALLY upsets me. Really. My portions of food are big too. i just want to cry all the time. My legs are so thin :( My arms are so bony :(.. mum says people are just jealous but they're not. i hear people whispering about me sometimes and it's horrible. I hate me.