Is it just me or do bras cut off your circulation too?

ok so heres my problem: im completely and totally flat but i cant just go around not wearing a bra (im 14). Whenever i go to victorias secret, i pick out the smallest bra available: 32A. what i thought was that the number (32) decides how big the band is. im not that skinny and this bra is extremely tight! when i try on a 34 or 36 the cups are way to big. my sister says it takes some getting used to and that ill wear into these bras but this is very painful and i have another bra that fits perfectly so i know its not impossible to find. I've worn that old bra so many times that now the straps are no longer white and there are holes in it. i dont think ill be able to get used to wearing this bra, ive worn it the whole day and every 2 seconds i think about it. any suggestions? do you honestly think ill get used to a bra 2 inches too small for my ribcage?