My personal experience:  I nursed my first for 4 months exclusively......he
abruptly quit and it took 2 months for my menses to return.  I nursed my
second for 26 months...when she was 15 months old I began to spot (nursings
were fewer)...with a history of very heavy menses and a dislike of them
totally..I quickly encouraged her to feed more often.  She of course had no
qualms about that and the spotting never resumed until she was almost weaned.
Sharon Lemon