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" &amp;quot;How do you know if your period is regular or irregular? I can&amp;#039;t figure mine out!&amp;quot; Laura, 17, Culver City, CA The fact that the word cycle is used to describe a menstrual period makes it seem as though it happens like clockwork every four weeks. But the truth is that there is a lot of normal variation in cycle length. A girl&amp;#039;s monthly cycle -- the number of days from the start of her period to the start of the next one -- is, on average, 28 days. But cycle lengths vary -- some girls have a 24-day cycle, some have a 34-day cycle. And it&amp;#039;s not unusual, especially in the first two years after beginning menstruation, to skip periods or to have an irregular menstrual cycle. Other things that affect cycles can be diet, stress, and exercise -- and occasionally illness.   If your period isn&amp;#039;t coming regularly, is especially uncomfortable, or has stopped (if you are sexually active this may be a sign of pregnancy), you should see a health professional. Most of the time, though, some variation is normal. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.seventeen.com/health/sex-health/q-and-a/a197/shqa-060707-2/>