The information supplied is not enough. Your height & weight are important information.Genetics plays a role. If you are tall, size is not that big. If you are overall overweight/obese, reduction in Fat/Weight will also reduce breast size. Do cardio, aerobic exercises, chest workouts like half dips, pushing the wall exercise etc.Gentle Local self massage with olive or coconut may help. Use ginger & green tea. Other options available are to consult an endocrinologist or a Surgeon (If you wish to go for that, however not recommended as of now)
Next Steps
To follow the above advice & not to be unduly concerned about it