Hi,

Your period stays away because the hormones your body makes in reaction to the suckling and in order to make milk (principally prolactin but there might be others...Barb?) inhibit ovulation. Without ovulation no endometrial layer (womb lining) builds up and thus it doesn't need to be shed, with a period. When prolactin levels drop low enough ovulation and AF return.

For some women ANY breastfeeding, even one feed a day, is enough to keep AF away, for others (myself included! ) even BFing 10-12 times a day and never having a gap more than 4 hours is not enough to keep AF away (my AF came back when DD was 6 weeks old, she was exclusively breastfed for 5.5months). It comes down to the individual woman and how sensitive to prolactin her systems are.

Some women who are NOT breastfeeding can have abnormally high prolactin (often associated with a tumour on the pituartry gland) and are infertile because of it.