I don't have any words of wisdom but I didn't want to be just a view. Big hugs, mama. I'm going through a nursing strike induced by illness with my 13 month old DD and I know how hard it is.
Congratulations on your pregnancy and I hope you and #3 have a long and happy nursing relationship!!
I've also heard that magnesium supplements can prevent period-related supply dips.
Finally, if your period returns because your babe starts STTN or eating a lot of solids, co-sleeping (if you're not already) and going slow with solids might help. Unfortunately, some women just find their period returns earlier than others.