Gonna delete this in a few hours for obvious reasons but--

It's probably correct! I wore a 36DDD for years and felt fine, but that was also all I could find in stores. Measured myself a few years ago and got 34H as a result. I ordered some from online (most retailers will have a sizing guide with US/UK size conversions) and oh. Turns out I'd had no idea that bras could fit because I'd never actually worn one that fit. My posture looked immediately better (and has improved), the bras are more comfortable, back pain I'd hardly noticed was suddenly gone, and they actually make my boobs look smaller (a good thing) because the breast tissue was no longer squashed and flattened to accommodate the shape of an ill-fitting bra.

Bra sizes are wack. The popular idea that DD = ginormous is not the least bit true (to begin with, cup size is just volume, so it's meaningless without a band size as well).

I get mine from bare necessities' website, mostly. They have fast shipping and decent sales every now and then.