Latching Issues - Please Help!

OK, here's the background on my situation:

• My little guy is three weeks old today. He was born 18 days early
• Right from the beginning he wasn't latching properly and because he was jaundiced he was given formula in the hospital
• I started pumping a couple of days later (I get about 90ml/3oz per breast per session)
• I have very large breasts and pretty flat nipples which probably makes latching difficult
• Whenever I try him at the breast, he seems very interested but just won't open his mouth wide enough and gets distracted easily
• The odd time I am able to get him on he either sucks a couple of times and then stops or doesn't suck at all. And he's definitely not getting much more than the nipple in his mouth (in spite of me doing the boobie sandwich every time)
• I saw an LC who recommended we get his tongue tie released, which we did when he was six days old but unfortunately it hasn't made much of a difference
• I've since seen three other LCs none of which were able to get him to latch for any significant period
• I've tried using a nipple shield which helped him latch brilliantly but it made my supply drop drastically so I stopped
• In the last couple of days he's been latching a bit more (maybe about five minutes at a time). Problem is his latch isn't good. I can tell it's shallow and he seems to be chomping down hard with his gums
• The pain from his chomping is excruciating and lasts well after I've taken him off the breast. The pain is both on the surface of the skin and deep inside the breast behind the areola
• When I take him off the breast, I can see that he has completely flattened it with his gums. He does the same thing with the bottle nipple

So the problem now is that I'm in so much pain from trying to breastfeed that it's even making pumping difficult too! I feel like I'm suck. Any and all advice from you seasoned breastfeeding vets would be greatly appreciated!