I had borderline anemia during pregnancy and low supply again. I've noticed that most of the items they tell you to eat to boost supply are high in iron: oatmeal, seaweed, fenugreek. So I started upping my iron supplement again and have sucessfully stopped supplementing.
I don't know if this will work for everyone, and I don't want anyone getting sick taking too much iron, but I thought I would share my theory.