Raspberries like a VERY acid soil. My guess is that your PH isn't low enough.
Try fertilizing with Miracid this fall and next spring and mid season.
Jeff David
Might also be that your plants are just immature. It takes a good year
for healthy strong roots to develop that can support a lot of big,
well-bearing shoots.
Good luck. There's nothing quite like a two-quart bowl of fresh-picked
ripe raspberries...
Alan Silverstein