I never had a issue with milk supply with our kids, but I also never nursed them either. When our third was born, I had and have a great supply for breastfeeding, but not AS much for pumping. But, I found a solution for that by drinking Gatorade!
We don't bed-share, so nursing while I'm half asleep isn't happening. So, from the start aside from the hospital where I only nursed, I make 4 ounce bottles for our son to have after 11pm and usually in one pumping session I just stop once I have the 4 ounces I want in a Medela 5 oz bottle and call it a day.
Well, a few moms on Facebook told me to drink lots of Gatorade (3 - 4 bottles of it through the day/evening), drink water, and eat oatmeal (flavored is fine) to increase my milk supply for pumping. Well, what do you know Gatorade worked like a charm! Now, I get 4 oz from one side and 3 oz from the other side sometimes. I usually pump at 4 or 5am when he gets up to eat (right before I nurse) and again at 7am or so usually. I don't pump much, but drinking 3 Gatorades a day helps so much! I do sometimes eat more oatmeal than other times.
I was told to drink 1 GALLON of water a day, so I will be using a gallon milk jug once my husband drinks the rest, and cleaning it out to use it for water only for me. I'm not one that's too keen on drinking water, so I might add flavor to it or just leave it be; I don't know yet.