My period is very regular. im not pregnant. but im 3 days late. and i have all period symptoms. what could be wrong?

It happens sometimes: In a woman with regular periods, some causes of a late period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (like birth control pills), hormonal imbalances, etc… Having a late period just once in a while may not mean anything wrong. Seeing a doctor is a good idea if symptoms are persistent, recurring, or worrisome.