Sometimes the breasts don't "let down" easily. Letting down is when the breast tissue loosens up to allow the milk to flow freely. Try placing nice warm towels across your breasts 15 mins. before feeding. The heat will cause the breast tissue to relax and the milk should flow easily.
Another technique is to take the breast between your hands and gently massage starting from the body and working toward the nipple.
One of the results of the breast not letting down is that the baby drinks the milk closest to the nipple; but, the milk in the rest of the breast does not descend to take over that space. Go all over your breasts looking for firm lumps - these are the milk nodes that produce the milk. If they are not routinely emptied, you can become engorged - very painful.
Hold the breast from the underneath and starting from the nipples, search for these nodes and massage gently when found. They will soften as the milk is moved out of them. Occasionally, take both hands and gently slide them down the breasts exerting a small amount of pressure to move the milk toward the nipples where it belongs. Don't worry if you express what seems to be a large amount of milk. The breast will replace it in time for the next feeding.