There really isn't anything, because it's the Prolactin that affects ovulation...which affects your LP. It usually lengthens gradually, by a day or two with each post partum cycle that you have....but some women find that it just stays short until after they wean.

When happens, it can mean making a tough decision about whether it's more important to keep nursing than to TTC or whether TTC is more important than continuing to nurse. There is no right answer to that one, it's very individual!