Why Am i flat chested i am 13?

I am so flat chested, its usually okay, but like, when we are getting changed for gym and stuff theres all my mates wearing all these mive bras, and then theres me, flat as a bored, and it feels quite intimidating sometimes if you get me..I know i'm young and "i shouldnt be worrying now" but its really lowering my self esteem, i dont exactly wanna tell my family either, they wont help. And also, my mates sort offf tease me about it, like at partys and stuff they are like wearing these short i mean MEGA short dresses and there i am not being able to wear like A size 8 because i have simply no at all, and also im naturally skinny, im about 5st 9, so yeah, i take after my auntie, but she has , and my mums a good 36C-D. PLEASE HELP! :[ and like i dont want comments just saying oh theyll grow, cus ill just ignore them :l