Can you have milk in the breast and be pregnant?
This is possible, but not common.
Most women that breastfeed their baby do not ovulate and hence
does not become pregnant.
When trying to wean the baby off breast milk, this reduces the
hormone production and production of milk slows down. At a stage
during this, ovulating starts up again, and you can get
pregnant.
Some few women do ovulate when breastfeeding. It is not a "fail
proof" method of contraception. Only fairly safe :-)