100% flat chested at 15!!! I don't know what to do!?

I am a sophomore in high school and i have never even worn a bra. Not even a training bra. The closest thing i have ever worn is this tiny cami. All my friends developed into C's and B's years ago, and i still have absolutely nothing. My mom is even worried about it, and she doesn't worry about this kind of thing.My luife is miserable and embarrassing. I don't fit in anywhere. Going dress or swimsuit shopping is miserable for me... i fill NOTHING out. I am a size 12 in KIDS!!! and i can't fill even THAT out! someone help me!