I just found out recently that apparently I've been a C cup for years, after resolutely trying to pretend I was a B. (Because that's what I was in high school, dammit! ...yeah.) I'm now grimly contemplating how to buy decent bras. Finding ones in my size should be trivial, fortunately; finding ones that are comfortable seems to be a completely different matter.
I had never before realized that I was supposed to worry about my funky underarms, though. Probably because I wear horrible one-size-fits-most bra...things...that don't so much support as wrap a layer of fabric vaguely over the whole area and call it a day.