Why are my so small?

i really dont understand. all my friends around me are Bs and up. and the hereditary thing makes no sense either. my mom and all the girls on her side (i asked) had at least Bs by 13. (Im 14, btw) on my dads side, they had Bs by 14. my mom was skinny as i am but it still doesnt explain anything. i dont have my period and im just wondering if theres something wrong with me? im a small 32A (ive done gymnastics since i was five, i work out, and did bball, soccer, and track. does thats make a difference?) and is there a way to speed up growth? thanks!