But anyway, breast size has nothing to do with milk production. Breasts usually grow some what as they prepare to make milk during pregnancy and of course many moms experience larger, fuller breasts in the early weeks of milk production. But it is entirely normal for breast size to reduce or for mom to start feeling "empty" while mom continues to make milk and it usually happens around this age. Also the return of fertility does not mean a mom is going to see a decline in milk production. Many moms get their periods in the early months of breastfeeding and continue to breastfeed.