First I want to thank all you ladies for your support.
Having shields that are too big or too small can make it harder to get the milk out. You could try different shields for a few days to see if it helps. Also get your pumped checked to confirm it is at peak suction.
I do breast compressions and apply hot compresses while I pump to help get the milk out. I double pump hands free but do compressions over or under the bra one breast at a time. I found it better than hand expressing but everyone is different. When I used the Medela pumps, I found I had to constantly reset the cycles and increase and decrease suction to get a let down. You could also try a different pump brand to see if you get better results. I had better results using an Ameda pump since it has adjustable cycling but other moms would say the opposite. Everyone is different so sometimes you just have to keep trying different things until you find what works for you.
Your body is constantly making milk so the breast is never completely empty. If you find the flow never stops, just keep pumping until you've collected enough or until you have to take a break.