I've also read that once your baby goes for a 6 hour period with no breastfeeding, it is no longer any use as a contraceptive. It doesn't guarantee when your periods will come back though, unfortunately, that just seems to vary wildly. Mine came back when LO was 5 months old while she was still exclusively BF'ed although she was sleeping about 10 hours a night at that point. I was very relieved because we were also wanting to have another one quite quickly - I was pregnant again by the time she was 6 months old - weren't expecting it to be quite that quick!! The thing is, the first time you ovulate you will not know about it because it'll be before your periods come back, so there is a chance of getting pregnant before your periods return and therefore them not returning!