Zucchini have male and female flowers on the same plant. If you don't have both in bloom at the same time you won't get zucchinis. If you look at the blossoms you should be able to see the difference in the structure of the blossoms. The female blossom has the beginnings of the fruit directly behind the blossom. the male blossom has a pointed pistol in the center of the flower. Be patient and the blooming of both will coincide shortly and you'll start getting zucchinis.