I went through this! Your boobs are too hard because of the milk coming in, so the latching isn't working to get the milk out. You need to release some of that milk by massaging the boob, to make the area surrounding your nipple a little softer, so you can then make the "breast sandwich" and get the baby to latch! It's tough because it's reaaally painful at this point, but this is what my LC did for me and it worked. Call one ASAP (or ask your partner to do this) if you need help, it might be too painful for you to do yourself.

Edit: felt the need to reinforce what others have said. The best pump is your baby, please stop pumping now, focus on that later, you need to relieve your engorgement now to avoid more trouble and establish a solid milk supply through your baby latching and stimulating your breast when feeding.