Male flowers are produced before female flower. So that could be one reason you have no fruit. Early in the season female flowers may not have developed yet.
For fruit to set, pollen from male flowers must be transferred to the female flower. This is done by bees whether native or honeybees. If no bees are present there will be no fruit. If few bees are present and pollination is poor, the result will be few and misshapen fruits. Drought stress can also cause misshapen fruit if bees are plentiful.
Male & Female Flowers
So how do you tell a male flower from a female flower? This is easiest to do in squash. All female flowers have a miniture fruit at the base of the flower.
The stigma of the female flower of a squash.
The flowers of this particular pumpkin are very large so it is easy to see the bulge or ovary of the female flower.
Male flowers have straight stems with no bulge at the base.
A male squash flower with the stamin that produce pollen in the center. Bees are busy at work in this flower. The pollen will stick to the bees and transfer the pollen to a female flower.
Notice that the stem at the base of a male flower is straight with no bugle or fruit shaped ovary. Male flowers are viable for only one day.
After a day the flower shrivels up and dies. Each day new male flowers open.
In cucumbers and melons, male flowers have very short stems and grow in clusters of 3-5 flowers. There will be an abundance of male flowers and very few female.
Another male flower
Notice at the base of each male flower is a straight stem.
Female flowers grow individually on longer stems with an ovary that resembles a miniature cucumber at the base. They are hard to find because the male flowers out number them.
I had to hunt to find this female cucumber flower.
A pollinated female flower of an Armenian cucumber.
An immature pickling cucumber. You can see the shriveled flower at the end.
If bees are not present or too few in number, then hand pollinating is an option. Pollen is yellow and produced in the center of the male flower. Use an small paintbrush to transfer the pollen to the stigma of the female flower or tear off the petals of the male flower and roll it in the center of the femal flower.
Gather the pollen from several different male flowers. Use only freshly opened flowers. This occurs in the morning.
Hand pollinating cucumbers can be tedious. It is often difficult to find female flowers.
If you provide a water source, lots of nectar producing flowers that attract pollinators, and have healthy cucumber plants you are less likely to have pollination issues.
Reasons for Poor Pollination
The fact that the individual flowers of cucrubits remain open only for a single day means they must be pollinated that day or the flowers drop from the vine. If the weather is not favorable for bees then flowers that open that day will not be pollinated and set fruit.
Bees are hard workers but do take off windy, rainy, or sometimes overcast, cool days. They prefer bright sunny days to do their work.
Many seeds are produced inside a cucumber, squash, and melon. Amazingly each pollen grain is responsible the development of a single seed. Numerous bees visit each flower to accomplish that task. Providing an environment attractive to both honeybees and native bees is helpful.
Avoid chemical pesticides and if using an organic spray do so in the evening after pollinators are finished with their work
Healthy cucurbit plants are essential to set fruit. Powdery mildew, leaf spot etc can be prevented by trellising vines off the ground to allow for good air circulation.
Mulching around cucumbers and regular adequate watering are also essential.
Armenian and Summer Dance are my favorite varieties for slicing cucumbers. Most pickling cucumber varieties seem to do well.