Darn I had a huge post and I lost it!
How often are you pumping? Are you double pumping or one at a time? Hospital or consumer grade pump?
Double pumping brings in supply better than single. More prolactin. It also allows you to pump more in shorter amount of time, which is essential when you need to pump as often as you do to bring in supply!
How often are you pumping? It needs to be at LEAST every 3 hours, round the clock. The time between around 1am and 4am is crucial for prolactin levels. I tried to hit 1 and 4 am, 3 hours apart. Some women have to pump more often, like every 2 hours.
A Hospital grade pump is essential for bringing in supply by pump.
Don't get discouraged, you are doing great! I am surprised your LO is drinking up all your milk. They never gave my LO more than 48mL at once (he was a 33+5 preemie). He was getting his by NG tube if not by breast though, not a bottle. I declined bottles entirely. If the flow is too fast in the bottle, it can force him to drink more than he needs, overfeeding him and stretching out his stomach, making him eat more in the future. With a bottle, when they swallow, it creates a vacuum that floods their mouth with more milk, which they must swallow to keep from drowning, and thus it creates more vacuum and more milk and they end up gulping it all down, even with very slow flow nipples.
At 6 days or so, I was probably strugging to make 70mLs per session. By day 10, I was putting out closer to 140mL per session. By day 18, it was closer to 280mL. When I left the hospital, they sent me home with BAGS of frozen milk. I made WAY more than he drank. I had about 250oz extra when I left the hospital. But 100mL is GREAT at 6 days old!