Congrats on your new baby!
Here's what I found on the internet:
It has been well established that breast-feeding has a contraceptive effect by delaying the return of ovulation. The underlying mechanism is believed to operate through an ovulation effect of prolactin and other hormones secreted in response to the infant's suckling. The high levels of prolactin in the mother's body stimulate the ovaries to maintain a high progesterone level. As a result of this, the return of menstruation 1s delayed anywhere from eight to eighteen months. This is good for the mother as her body's iron is conserved. A lengthy absence from menstrual periods following childbirth 1s called lactation amenorrhea. Not having periods during pregnancy is termed pregnancy amenorrhea. Many mothers have relied successfully on breast-feeding during amenorrhea as a method of natural child spacing, and some mothers have experienced some infertile cycles after the return of menses. However, some nursing mothers have conceived without a return of menses. Present research seems to indicate that the risk of pregnancy during lactation amenorrhea (prior to the first menses after childbirth) is about 6 percent. Thus, lactation amenorrhea is a health asset to the mother in her childbearing years. Breast-feeding eliminates the need for drugs and prevents breast cancer.
As many fully breastfeeding mothers know, lactational amenorrhea (absence of menstrual periods as a result of breastfeeding) does affect their ability to get pregnant. Scientific data supporting this has been mounting for years. The Bellagio Consensus Conference on "Breastfeeding as a Family Planning Method" established that fully breastfeeding mothers who remain amenorrheic have less than a two percent chance of becoming pregnant in the first six months postpartum. "Fully breastfeeding" is defined as supplementing no more than one or two mouthfuls a day and waiting no more than four to six hours between nursings. A woman who is practicing the Lactation Amenorrhea Method (LAM) relies on exclusive or nearly exclusive breastfeeding for postponing or avoiding pregnancy during the first six months after childbirth or until her periods return, whichever occurs first.
Many breastfeeding mothers find they remain amenorrheic longer than six months, especially mothers who practice a style of nursing that Sheila Kippley calls "ecological breastfeeding." In Breastfeeding and Natural Child Spacing, Kippley describes ecological breastfeeding as the kind of nursing that most effectively spaces babies: nursing on cue, keeping baby close, providing all nourishment and liquids at the breast for the first five to eight months, and nursing to comfort the baby. It does not include the use of bottles or pacifiers, mother-baby separation, parent-imposed feeding schedules or restriction of night nursings. All of these practices limit the nipple stimulation that suppresses ovulation.
The chance of pregnancy occurring during the first three months of ecological breastfeeding are practically nil. During the second three months, there is a less than 2 percent chance of becoming pregnant before the first menstrual period. After six months postpartum there is a six percent chance of becoming pregnant before the first period. That means that an amenorrheic woman who is relying on ecological breastfeeding alone has a 94 percent chance of not becoming pregnant during the second six months postpartum.
Women who practice ecological breastfeeding average 14.6 months of amenorrhea. Seven percent experience a return of their menses in the first six months following childbirth. Thirty-seven percent get their periods back during months seven to twelve. Forty-eight percent get their periods back sometime during the second year after childbirth. Eight percent go longer than two years without periods.
Despite the variability in the return of menses, there is not as much variation in the return of fertility as might appear. Women who experience a return of their periods in the first six months tend to be infertile for a few cycles, while the early cycles of women experiencing a longer period of amenorrhea are often fertile.
I hope that helps!