I understand why you are using the nipple shield, I had cracked and bleeding nipples early on (even with perfect attachment!) and I used the shields as well. One of my mates is a MCHN/LC (I'm loving having endless access to her LC knowledge!) and she told me that while the shields were ok for a couple of days while my nipples healed I needed to get rid of them as soon as I could. She explained that the nipple stimulation by bub's tongue tells the brain to tell the breast to produce more milk. This stimulation is blocked when using the shield and supply decreases. That's ok for some women who have an abundant supply, but I did not! If you can find a comfortable position, maybe try to feed without the shield.

It's hard isn't it, when you don't know how much they are getting? Our nipples should give a digital printout after each feed! Sounds like you are doing a great job.