I think Stacy's right about your body's own timing. I've read that those practicing "ecological breastfeeding" (i.e., cosleeping, night nursing, nursing whenever baby is hungry, not adding solids until the baby shows an interest in the food on your plate) have a return of menses on average at 14 months postpartum. But it takes a wide range to make an average. And I had my periods resume at about that time (13.5 months postpartum), but had stopped cosleeping at 2 months, introduced solids at 5 months, stopped night nursing and dropped to 4 feeds at 9 months, and finally dropped down to 2 feeds per day at 12.5-13 months (I think that's what finally did it). So I was by no means practicing "ecological breastfeeding", but had similar results. And it sounds like Stacy was practicing ecological breatfeeding for her first baby, and had her periods resume at 4 months. So I think we all have a timetable predetermined by our bodies that we may be able to manipulate somewhat, but not completely overrule.
If you're interested, there's a book called "Breastfeeding and Natural Child Spacing" by Sheila Kippley that talks a good deal about using breastfeeding as birth control. But I don't think I'd trust it completely once I no longer met the criteria for LAM.