Boobs getting smaller? ?

So Im 18. And ever since I was around 16 weeks pregnant I noticed my Boobs were shrinking. Which is weird cause I thought it was the opposite when you have a child. Now I gave birth eleven months ago.. And thought ok my Boobs have to grow now. No. They keep getting smaller! I was a full c. Almost D. Now Im a small c cup :/ very discouraging. My chest was my pride and joy lol. It made me feel Idk womanly. Now I feel small and Idk weird. So what could be doing this?