mine didn't return until >13 months!

BREASTFEEDING AND FERTILITY

"I've heard that breastfeeding can keep me from getting pregnant. Is this true?"
Yes, as long as you nurse according to the rules of natural child spacing. The same hormones that make milk suppress the release of reproductive hormones. While breastfeeding full-time most mothers do not ovulate and do not have menstrual periods. This means that you can't get pregnant, at least for a while. It's as if your body is telling you, "Nourishing one baby is all you can handle at the moment. It's too soon for a sibling."

"How reliable is breastfeeding as a natural contraceptive?"
You have to follow the rules of the game to get the full benefit of breastfeeding's effect on fertility. In the last ten years, lactation researchers have developed the lactational amenorrhea method of family planning, called LAM. Research shows that LAM's effectiveness in preventing pregnancy is better than 98 percent, a figure that compares well with artificial methods of birth control. According to LAM, a mother can rely on breastfeeding for protection from pregnancy if she can answer "no" to the following questions:
Have your menstral cycles returned?

Are you supplementing regularly or allowing long periods without breastfeeding, either during the day (more than three hours) or at night (more than six hours)?
Is your baby more than six months old?
Studies have shown that most mothers who are breastfeeding exclusively remain infertile for more than the six-month period covered by LAM. Ovulation and menstruation return only when the baby starts to nurse less often and prolactin levels fall.

4 TIPS FOR USING BREASTFEEDING TO DELAY OVULATION
Practice unrestricted breastfeeding without regard to schedules. Usually six to eight breastfeedings a day will suppress ovulation.
Don't train your baby to sleep through the night. (The milk-making hormones that suppress ovulation are highest between 1 a.m. and 6 a.m.) Nighttime nursing is important to the suppression of fertility. Sleeping with your baby facilitates unrestricted feeding at night.
All of baby's sucking should be at the breast, for comfort as well as food. Avoid the use of supplemental bottles and pacifiers.
Delay the introduction of solid foods until age six months or later. Solids should provide additional nutrition, not substitute for breastfeedings.

The key to using breastfeeding to delay the return of fertility is frequency of breastfeedings. Because prolactin clears so rapidly from the blood, frequent feedings are necessary to keep it high enough to suppress ovulation. As baby nurses less frequently, prolactin levels fall, reproductive hormones rise, and fertility returns.

If you follow these rules, you may enjoy a period of lactation amenorrhea (no menstrual periods) that lasts thirteen to sixteen months. In fact, research has shown that women who practice natural mothering according to the above rules will average 14.5 months without a period following childbirth. Remember, this is only an average. A few mothers will experience a return of menstrual periods by six months, others not until two or three years.

When menstrual periods return, the first one is often anovulatory, meaning that it is not preceded by ovulation (the release of an egg), and thus you could not have gotten pregnant before this first period. However, about 5 percent of women do ovulate before having their first period, and the longer you have gone without having periods, the more likely this is to happen. Thus it's possible to become pregnant while breastfeeding, even if you are not menstruating. Once your periods resume, you should assume that it is possible for you to get pregnant, and you should take precautions if you don't want to add another child to your family in the near future. This might be a good time to learn about natural family planning methods, which enable you to determine exactly when you are ovulating and could become pregnant. Or you may decide to use another method of birth control as breastfeeding's effect on your fertility fades. See Couple to Couple League International at www.CCLI.org.

Sometimes women who are nursing older babies or toddlers want to get pregnant and find this difficult while they are breastfeeding. The baby's nursing may continue to affect a woman's fertility even after her periods have returned. This can be very frustrating. Sometimes getting the toddler to cut back a bit on breastfeeding, especially at night, can make it possible for mother to conceive.

from Dr. Sears website

13 months pp for me, too ... it was loverly while it lasted.

oooh someone should be talking to women like my grandmother (mother of eight) who exclusively brestfed her kids and was constantly pregnant --her kids are all born about a year apart... they didn't have or use contraception and she just kept getting pregnant while breastfeeding