Sounds like a lack of pollination.
You can hand pollinate to overcome the problem. Here are the male and female flowers. Probably not of your variety but they're basically the same across the board.
Male on the left. Female on the right on the end of what looks like miniature fruit. It's actually an ovary that, when pollinated, will grow into a fruit.
Both flowers open in the morning and will often close again during the day. Once closed, they don't open again. The female flowers have to be pollinated while open so it can mean getting up early.
Remove a male flower from the vine, stem and all. Carefully remove the yellow petals to expose the stamen inside. It will be coated in pollen.
This is roughly what the female flower will look like inside. That's the stigma in the centre:
Brush the stamen against the stigma to transfer the pollen. Don't be too vigorous. Damage the stigma and odds are you won't get fruit.
It's a pretty simple process and good fun!