There are several reasons why your tree may not be producing fruit and without more detail it is hard to say what the cause is in your specific case.

Where are you located? How is the weather in your area right now? Temperature?
How old is the tree? When was it planted?
Do you fertilize the tree with anything?

The tree may have disease or there may be insects or other pests attacking it. Are there any symptoms other than the lack of fruit developing that would cause you to suspect a disease? Are the leaves green and healthy?