Sometimes one breast grows faster than the other, and no one else even notices. Breasts that grow quickly can develop stretch marks, which will lighten with time. It is normal for your breasts to feel discomfort right before your period. Breast issues are very uncommon in teenage girls. It is imperative to know your breasts. The method for doing so is to lie supine (on one's back) and touch your breasts. Apply pressure with your opposite hand in varying degrees around your breast. Doing so will help you notice any differences in your breasts. Breast cancer can happen with any size breast. You should tell a trusted adult if you experience discomfort in a breast that is not near your period, a swollen area, a firm lump that remains the same all the time, or liquid leaking from your nipple.