Decreased vaginal lubrication can occur while breastfeeding. This is not uncommon, and it is caused by an increase in the production of the hormone called prolactin, and an associated decrease in estrogen levels. This condition reverses once menses resume, which restores estrogen levels back to normal. For some women, menses return even while breastfeeding. For others, menses and the resulting return of normal estrogen levels does not occur until full weaning.