ANDY'S ANSWER: Assuming that you're a girl, I would have to say that your body just isn't ready yet. The first signs of breasts growing are usually a little swelling of the areola. This is the brown part around the nipple. At this point in time, it's probably too early to be wearing a bra, but you will know that your breasts have at least started to grow. If your mother has very small breasts, you may have inherited her physique, so you may never be really large busted even when fully developed. You didn't mention your age, but if you are under 15, you're still well within the norms for puberty. PATIENCE, grasshopper;-)
Below is the recording of Andy answering this question.