When does girls breast produce milk?

Breast milk is only produced during pregnancy and after the baby has born.
But it is not unusual for a girls boobs to feel sore or tender when she is on her period. Hope that helps.

Producing breast milk. Or lactation. Has nothing to do with menses or sexual excitement. It has to do with hormones produced during pregnancy that ready an expecting mother for breast-feeding their child.

Check out this easy to read site. Http://en. Wikipedia. Org/wiki/Lactation.