Sometimes hormone changes happen later on in life that can contribute to things such as your breasts growing. Like when you are on your period, they can get bigger due to hormone changes, sometimes when we reach different stages of life our hormones are affected and can do many things to us! Oh also, sometimes when I am losing weight my boobs seem to get bigger but this is really because I lose weight around my arms and my ribcage before much else, making your boobs look bigger.