How to tell mom that I need a bra?

I'm 14 and going into high school next year and I really need/want one... I'm like a 34b and don't have one I have no idea how to ask my mom because she's been stressed a lot... I wear these bra things that are bally total fitness from Costco that she brought me awhile ago... But I still show through sometimes even when I wear Camus or stuff on top... Plus my mom isn't the shopping type either so I have the same problem with makeup... What should I do? Just ask or deal with it? Plus I never have time to ask because my lil' bro is always around