Shanetastic, you have some years before you have to worry about getting fat instead of gathering curves.
I started to gain unwanted weight when I went from a pretty active job to a desk job.
I gained more when I passed 35 years old.
And since I have been on HRT I have gained *lots* of weight. The things that we wish to have, things like a smoother face, breasts, hips, bum, whatever, they all add weight. Go from flat-chested to a C-cup and you'll see some weight.
There is additional weight in the tissue needed to support what I call the "supplemental circulatory system." When breasts form they need a blood supply, as does the tummy fat, however little one might gain. It's easy to see these new blood vessels in the mirror.
I'm not so sure that I would be concerned about gaining weight at this time.
I hope that this helps.
Wing Walker