[Doll]

This is natural. Your breasts will be at their smallest on the fifth day of your monthly (or around then). This will likely happen every month. Most girls who aren't even on NBE experience this naturally. It's due to your hormone levels changing during your cycle.

Permanent growth takes time, so you may go through this a few times before it finally sticks. But don't give up! The fact that you saw any growth to begin with means good things will come.