Talk to your dr there is med that can help
Stay hydrated - that always helped me. I've heard of things like eating oatmeal helping. For me whenever I had my period my supply would take a hit. Just keep working through it and keep a consistent pumping schedule. Best of luck!
You could also try fenugreek or blessed thistle, they are natural herbal supplements that you take like a vitamin.
There are lactose cookies that are oatmeal bases with other things like brewers yeast and such that will help increase your supply.