Once this bleeding has stopped, you may notice that your first period after you have a baby follows fairly shortly, usually within a few weeks. About 70% of women who are not breastfeeding will have their period by 12 weeks postpartum. If you are nursing you will typically not have your normal period for many months, depending on the amount and frequency of nursing and the amount of supplemental feedings, if any. The risk of ovulating in the first six months after having a baby, while you are breastfeeding, is about 1-5%. Some women use a method of lactational amenorrhea (LAM) as a means of birth control.
Obstetrics: Normal and Problem Pregnancies. Gabbe, S, Niebyl, J, Simpson, JL. Fifth Edition.