It could be a pollination problem or because the plants are still young..Cucumber plants, like squash, melons, and similar plants have separate male and female flowers. The female flower has a small fruit behind it, the male don't. The male flowers produce the pollen needed to fertilise the fruit on the female flower, but they do not produce the fruit. The female flower don't produce pollen but need it for the fruit to develop. It is therefore dependent on a pollinator - usually insect to bring the pollen from the male to the female flower.
Male flowers start to form before female flowers but as they do not carry fruits, it is not unusual to have a profusion of blooms at the start of the flowering period, and no fruits. This period vary depending on the plant variety and growing conditions.
If the problem is lack of pollinators, you will see female flowers on your cucumber plants, but they will not start to swell and will often turn yellow and fall off. Pollinators are usually honey or bumblebees, but other inects such as solitary bees are also good pollinators. In the past several years we have had various problems affecting the honey bee populations. However, bumblebees and other inscts are also good pollinators for these plants. Small, native ground bees are also good pollinators. Some years pollinators have been slow to appear and there have been issues about the reduction in the honey bee population in recent times and the use of pesticdes can damage habitat for other pollinators.
You can hand pollinate your cucumbers by hand as an alternative. Remember the flowers re only fertile in the morning of their first day. In the morning collect pollen from the stamens at the center of the male flowers and then transfer it to the stigma at the center of the female flowers. Any small paint brush with a soft bristle will do the job adequately. Success should mean you start to see the fruit swelling into recognizable cucumbers in a few days. Hopefully the normal pollinators will reappear shortly if this is the problem.