What Causes Delayed Periods?

Hello doctor, My wife have taken Duphaston due to delay of periods for more than one month. We have cross checked if she is pregnant or not. But she is not preganant. Doc said that wait for 2 weeks. We have waited for more than 2 weeks. But she didn t get her periods. And we again checked for pregnancy. But she is not. Please help what could be the problem and how to get over it. Thanks