My period has been delayed for 4days now and it's happened like this before. i'm not married so please what could be the cause and what do i do?thanks

Marriage vs menses: Just because someone isn't married doesn't mean that her menstrual cycle will be regular. Many women have irregular menses. However, unprotected sexual relations can lead to pregnancy which can then delay one's periods for upwards of 9 months! if you don't want to have children now and need a regular cycle, ask about oral contraception or birth control pills. However, these won't prevent infection.