I've gone from a B cup to an E, within just a few months - at 27!! I thought it might be because I gained a little weight, but I've now lost about 28lbs and my chest hasn't shrunk at all. I've gone up and down in weight before but never moved up from a B. So I too wondered if it was a med side effect, but didn't find anything when I Googled it to suggest that... I did, however, find some info that suggested that women who haven't fully emotionally developed also may not have fully physically developed in that area... so I can't help but wonder if my progress in therapy has something to do with it (I've been in therapy just over a year now). I also read something about when you have a connection with your therapist (in my case the first person I've felt 'connected' with), it can cause the release of oxytocin - the 'cuddle' hormone - which apparently is the hormone released during pregnancy that causes the breasts to grow.

That's my theory, anyway! But like, maybe don't quote me on it...