Have you seen the flowers early in the morning or during an overcast day? I bet they've opened when you're not around. If the flowers aren't pollinated the fruit will not continue to grow after the flower shrivels up.

To self-pollinate, I remove a male flower (the ones WITHOUT a small squash at the base of the stem), peel away the petals (leaving the pollen-covered area exposed), and rub it inside the female flowers (the ones WITH a small fruit at the base).

Good Luck! Amber

Here is a link that might be useful: Hand Pollinating