Domperidone/motilium can mess with your cycles. That's only really anecdotal though. I've talked to a lot of people who are taking it for low supply and most have reported AF staying away, so
It does indirectly increase your prolactin so maybe that's why.
Some of the BF supplements aren't good for pregnancy, Blessed thistle comes to mind. Some are more ok than others. There's a book called Motherfood that talks about lactogenic foods and talks some about what's ok to take during pregnancy and what isn't. I think...I don't actually have the book, though I do have The Breastfeeding Mother's Guide to Making More Milk which has a big section on galactalogues.
Things like alfalfa and red clover are galactalogues ok for pregnancy (and I'll be taking them during my next pregnancy in hopes of making more milk).