Nurse Christel answers: Most women have irregular periods once or twice over a time span of several years. If you don’t have a period for three months, you should contact a doctor. As you should if you’re irregular over a longer period of time after having previously been regular. Stress, weight changes, worry, or travelling between different time zones are just some of the factors that can make your period irregular. Find out more about this in the articles under the heading, “Your body.”