Please read! Milk supply builders????

Hi, I have a question about nursing. My daughter is in the hospital right now. She has ti have a spinal tap done she's sick but we don't know what from. She's almost 3 months old, her birth weight was 7lbs.5oz and she currently weights 8lbs. The doctors are very concerned. And want me to substitute my milk. I don't want to. I Will if I have too but I dont want too. breastfeeding is a passion of mine and I have worked so hard to be able too. My breastfeeding journey has been more painful then me giving birth to her. I dont want to quit, I pumped when she was first born for a few weeks then she started latching, i was getting 6oz on 1 side. But here at the hospital I'm only getting 1 1/2-2oz. Idk if its because I'm stressed and worried. I didnt eat anything yesterday because of everything going on. I'm trying to build it back up. So I wont have to substitute. What can I do to get more milk FAST. My breastfeeding journey relies on it...