hi S.,
i started menstruating when my daughter was 2 months old and have had the same problem wiht supply ever since. i did some research on the internet, and discovered a few things that have really helped, maybe they'll work for you:
* start taking a calcium/magnesium supplement that's 2 parts cal to 1 part mag (the magnesium helps the calcium uptake in your system - there's some relationship between milk supply and calcium, but i have forgotten what it is...). they say to do this around when you period starts, but i could never remember so just have been taking it every day.
* both fenugreek and blessed thistle tincutres (you can get these at the health food store) worked wonders - take about a dropperfull or two a day around the time you think your period will start. literally - i'd go from flat to full in a matter of hours.
* I have a wonderful accupuncturist and chinese herbalist. she treated me with herbs and needle points, and that has also been a great help.
my daughter is now ten months old, and with the above treatments, i've only had to supplement with formula once or twice. the formula we use is called baby's only. you can get soy or milk based. it's organic. you can get it at the health food store. it's more expensive, but i figure we aren't using it that much so it's worth it to me.
good luck.