So that high levels of prolactin lead to either high or low levels of this other factor, which then affects fertility. Post-partum, a woman does not ovulation for a while, even if she isn't breastfeeding. The greatest level of suppression is not ovulating, but as your prolactin levels go up, your fertility will gradually return. It is also possible to ovulate without having the right hormonal levels in the right combinations for the uterus to have been preparing for implantation, so yes, it is possible to ovulate without menstruating. For all of these stages, there seems to be incredible individual variation between women.
Some women get pregnant again the first time they ovulate, with no intervening menstrual periods.
That is, if the baby nurses more frequently again,, after the mother's periods have returned, it would raise the mother's circulating levels of prolactin, presumably high enough to affect fertility again. I am sure that this works, both from personal experience and from anecdotal reports from other nursing moms. When he was 13 months old, and fall semester was starting, I put him in day care 6 hours a day, so I could have more time at the office, and my periods promptly returned the next month. I didn't have a period in December or January, then resumed again for good in February. You should consult a reproductive endocrinologist to see if this is the case.