What Causes Absence Of Period?

Hi m in japan now.And i am married.I am 22 years old with height 5 ft and 50 kg of weight.Dont have anyedical history.And this problem is first time.My mensuration period is not just happening.It happens in same date from past but this time it is still not happening as some semptoms of back pain is happening.please let me know what is happening to me.