Whats the pain from? Him nursing, or are they dry and cracked?
I've been told that BFing shouldn't hurt one the nipples are a bit tougher, and that if it is then it means they aren't latching properly.
What you're expressing is a lot! I express even 2 hours and only get 10mls at a time, so it take me about 4-6 hours to get 1oz.
I think if someone who knows your history is recommending shields then it might be worth a try. You need to be prepared for the fact that you may have to wean him off them though and get him to reaccept the nipple. However if it's a choice between giving up and shields, and you don't want to give up then try the shields.
I find shields hurt, but every breast is different so they may be easier for you.