I need to build up my milk supply

So I feel terrible. I had a great supply going while my baby was in the NICU. She had so much milk while there, and our freezer was full. Well baby came home and I got so into taking care of her all day and night that I wasn't pumping as I needed too and now my supply is terrible. (i.e. less than an ounce per side in a session) it wasn't too bad but she has started eating more and so now our freezer supply is gone and I'm pumping as much as I can but that is only giving one one 2 1/2 oz bottle per day. The rest of her bottles I am supplementing with formula for so she eats.. this is making her extremely fussy/gassy/ and just plain miserable. I feel like a terrible mom over this.

What can I do to up this again? I've been pumping back on a schedule now. Drinking about 100 ounces of water a day (literally drinking nothing else) eating oatmeal for breakfast.... I feel lost..