How to tell my body I need MORE!

Br

My LO is 5 weeks today and I'm having to pump and bottle feed due to poor latch and low milk transfer. I'm able to pump 2oz from the left, and one from the right, which adds up to 3oz, and just enough for the next feeding. I'm pumping every 2 hours during the day and every 3 hours after bedtime. I'm staying hydrated as well. How do I tell my body to up the volume?