My period is 4 days late, & it usually starts within a day or two of when it should. i had my usual pms symptoms, & ive been cramping as though it should be starting soon, but it hasnt. what could cause this, & when should i start to worry about it?

If you are sexually active, take a pregnancy test. Pregnancy tests will be positive as soon as the first day of your missed period. If negative, consider that Hormonal fluctuations can also lead to menstrual irregularities. This can be caused by stress, increase/decreased exercise, weight gain/loss, lack of sleep, ovarian cysts, etc. Talk to your Dr if the irregularities persist more than 3 months