I've tried many things to improve my milk supply during the pre-period drop. I've sought lots of advice here (and gotten some great ideas!), increased pumping that week, increased nursing that week, daily oatmeal, fenugreek supplement. All with little success.
BUT, when I started taking a daily supplement of calcium/magnesium (1000mg calcium, 500 mg magnesium), I saw real improvement. This was my first cycle doing this and I began the supplement at ovulation and continued to the start of my period, as recommended on kellymom.com.
Not only did I not see the dramatic dip n milk supply that I've seen in previous months (my periods returned a 3 months, and my baby is now 6 months old), but I noticed an increase in the amount of fatty milk in my bottles as well. By that I mean that when the milk separates into layers, the layer of dense milk at the top is much bigger than it used to be.
I know I'm just one case, but I think this type of supplement is worth trying for anyone having pre-period milk supply issues!