What Causes A Delayed Menstrual Period?

Actualy I was having my period regularly.Last month my date was 12th Feb,This month till now my period has not been started. What may be the reason?I did not have sex directly ever,but I had physical relationship to some extent with somebody 5 months before since 2 years. But in last 5 months I did not have any relationship with anybody and my periods were also regular



Please give me some idea regarding After a regular period till now and no physical relation since 5 months can sex or physical relationship be the reason for not being started my period?

Or it will get started normally?I should wait until when?