Medical causes of enlarged breasts?

I know the boobie jokes are inevitable, but I really am hoping for an honest, medical, GQ answer.

What are the medically accepted causes for an adult female’s breasts to get bigger? Is there any reason going OFF hormonal birth control would cause that?

Here’s the background: I’m just shy of 30 years old … long past puberty. I was on various birth control pills for about a decade or so. Two years ago I got laid off and subsequently lost my health insurance. I stayed on the Pill until the Rx ran out, then didn’t renew. So I’ve been off the Pill for … oh, let’s say a year, more or less.

About four or five months ago, Mr. Horseshoe and I both noticed that the girls have gotten bigger. His reaction, naturally, has been one of unbridled joy. I went up a full cup size, so my reaction has been tempered somewhat by the annoyance and unexpected financial impact of having to buy new bras and shirts.

It’s been several months now, so I know it’s not pregnancy (Og forbid) or hormonal swings from my cycle. No tenderness or pain. My overall weight hasn’t changed, though I’m not much of a scale-hopper. But my pants fit the same.

Soooo … I’m out of ideas. Doctor-y and medically inclined Dopers, do you have any others? If nothing else, I’d like to bottle whatever happened - I’d make a bloody friggin’ fortune. I’m still uninsured, so I can’t afford to go to a doctor for this, but I’d like to know if there’s any reason at all I should be concerned. I know that going ON the Pill often makes boobs get bigger, but going OFF the Pill? (FWIW I never noticed any differences at all in the girls while I was on the Pill.)

Are you sure about the possibly not pregnant?
Estrogen does stimulate breast glandular proliferation, while Prolactin stimulates milk production while Progesterone pretty much prevents lactation, but when you have the kid, your progesterone and estrogen levels drop, and thus Prolactin is uninhibited, allowing you to produce milk to feed the kid.

Then again, perhaps you’re just producing more of those hormones for another reason and causing the breasts to enlarge, in which case… if you’ve noticed any other unusual symptoms or changes from the norm, perhaps you should consider a doctor’s visit (things like tenderness, aches, pains, fever, night sweats, palpitations, or anything else outside of the norm).

Or it could just you’re gaining weight, but it’s going to your breasts, and not your waistline (if you’re not a scale hopper, and using your pants as a measure).

When was your last period?

(Meaningless question, but from my experience, that is what the gynecologist wants to know)

I’m sorry to say this but it’s probably your age. You should probably re-evaluate your diet and exercise setup, too, or you’ll put on weight elsewhere.

I put on 2 cup sizes at 30 within about 6 months. I bought new bras, and next thing I knew I was buying pants two sizes bigger too because I had some belly going on, which I’d never had before. I’m working on slowly dropping the weight, but unlike my pre-30 weightloss schemes, I now have to bust my behind exercising AND watch what I eat.