Why am i so different?

okay so all my friends are starting to have bigger . there all in sizes b already! im 13 and im still an A32 which i just barely fit in that. i wear pushup bras a lot but i dont like having fakes. :[ i know i should be patient and everything but sometimes get really jelouse and sometimes depressed im not developing at a normal pace.im pretty athletic an ive been on my period 3 or 4 times now and nothing has happened. what can i, or should i do to get them to develope? why arent i like most girls?