lol sweetie its nothing to be embarrassed about
boobies are boobies..girls have em...all shapes and sizes..so its not like its anything new
and of course in the process of getting on sometimes ur boobs arent exactly even..and usually ur dominant boob (for me its my right) its slightly bigger..lol anyway
im 15 too and i use to be shy but see i have 2 go 2 tha store w/ my dad..since my mom never takes me anywhere.lol.. but yeah..just get measured by someone who does it (i know ppl do it at victorias secret) and then get ur bra! its really not that bad and u shouldnt be ashamed...
it'll take a while..but dont worry..and ur mom WILL understand..she only got em too! lol
hope i helped