breast pain and bra size

[essos.livejournal.com]

This may sound like an obvious question but I want to confirm.

I pretty confident I'm wearing the wrong bra size, based on the simple facts that I haven't ever been fitted, I'm wearing the same size I did when I was 13 (I'm 20 now) and my breasts have definitely gotten bigger in the past six months (due to a BC switch and some weight gain).

So...this is why my breasts hurt at the end of the day, right? Being all bunched into something too small? And furthermore, what EXACTLY goes down when you get fitted?

Thanks!