One of the most common gynecological problems is an irregular menstrual cycle. But before you jump to the conclusion that you're irregular, it's important to remember that being regular doesn't mean your cycle is the same number of days each time. One month your cycle may be twenty-nine days and the next month it may be thirty-one days. This is still considered the norm. It's also normal to have a light flow one month and a heavy flow the next. Another common misperception about irregular cycles is that unless you have a period every four weeks (again, the statistical average) you're irregular. This is not true. Some women menstruate every three weeks, which is normal for them; some menstruate every five weeks, which is also normal for them. The only time you should be concerned is if your period consistently yo-yos: for instance, three weeks, then four weeks, then five weeks, then three weeks. When this happens, it's usually a sign that you're not ovulating regularly. This is common in young girls after they first begin menstruating. If your period jumps around once or twice a year, there isn't anything to worry about. Occasional stress is usually the culprit when this happens. 

Once in a while, women may skip a period and then experience a heavier flow with their next period. This is extremely common. Women who are trying to get pregnant, however, often fear that this is an early miscarriage -- so mild it feels like a heavy period. This is usually not the case. Although it's possible for a pregnancy not to take and be expelled in the menstrual flow, it's rare and occurs in less than 1 percent of women. In most cases, skipping one period is caused by skipped ovulation. The flow is heavier after a skipped period because the estrogen has been building up in the endometrium longer, and there is more lining than usual that needs to be shed. You would have built up two cycles' worth of lining, so the flow is naturally heavier than normal. That being said, you could have a lighter period or bleeding that fluctuates in duration or amount. 

The number one cause of a skipped period is pregnancy. Regardless of whether you've had sex, if you skipped a period, get a pregnancy test. If you're on oral contraceptives and have not missed a pill, the missed period is probably related to your dosage and can be remedied by adjusting the dosage. Another common cause of irregular or skipped periods is physical and emotional stress. One scenario is worrying that you might be pregnant and then actually missing your period because you're worried. Other stress-related situations revolve around career changes, job loss, a death in the family, going off to college, moving, exams, and stressful workloads. It's not really understood why stress can cause you to miss a cycle, but it is considered a protective mechanism, a sort of prehistoric parachute in the female body. The body senses the stress levels and somehow decides to stop ovulation for that month to prevent a "stressed" pregnancy. 

Overdieting and overexercising can also affect your cycle. For example, sudden weight loss could cause you to miss your period or cause a long bout of irregular cycles. Overexercising can also cause you to miss your period. It's not unusual for female athletes to stop menstruating when they're in training.