What Causes One Breast To Grow Bigger While Other Stops Growing?

I am 16 years old. I have uneven breasts. Now i know that yes they will not always be exactly even but I have a D size breast and the other is a A size. I don't know what to do and I heard that it takes till 4 years after you start your period to fully develop. I started my period kinda late at the age of 15. So its been about a year. But this one breast just stopped growing. What could be the problem? Could a problem or disease have stopped it?