I was curious about this too, so thanks for asking.
I'm so confused about what is going on with me. I thought you only staved off the periods if you EBF, and even then it was like 5-7 months before you have a period. I haven't EBF since DS was 2 months old (I do 50/50 BF and formula), and he is 4 months old, but no sign of ol' Aunt Flo. I wish I would have periods now so I can keep track and know when I'm ovulating to avoid getting pregnant (we like natural birth control - or none!). I need the old chart at hand to know when to avoid, but I can't do a chart without a period. So frustrating.