I heard a nipple shield helps a lot.

You can try to contact La Leche League International for extra help, or call the hospital you gave birth at and meet with one of their Lactation Consultants. As far as tips that I can give you, have you had him checked for tongue tie? If not, that could be the issue - it's common believe it or not. Call hid pediatrician and try to get him in there today to be checked for it and also to discuss the issue. You can try to give him a pacifier first and then do the 'bait and switch' where you remove it quickly and swap it for the breast. Keep offering him the breast every couple of hours. If you can pump in the meantime until he gets used to breastfeeding, it will keep your supply up.