So I recently got a $300 Medela double pump, and when I pump almost nothing comes out. Let down occurs almost immediately, but then stops after a couple minutes. Sometimes I pump for 10-20 minutes, and usually get only about 1 oz of milk (or less). I have no idea what I'm doing wrong. I want to be able to pump enough to feed my dd ebm all through the night, but right now it's not happening. Any advice?