Once women have been through puberty, they usually develop a regular menstrual cycle with periods that occur around the same time each month. Women’s menstrual cycles last on average 28 days, but can vary from woman to woman.
However, there are many reasons why some women may experience irregular periods. Some women find that they have periods early or late in their menstrual cycle; that they may last longer or shorter than usual, or that they may sometimes be heavy and sometimes lighter.
Other reasons for hormonal changes which can affect the regularity of your periods include losing a lot of weight or exercising too much. Stress and anxiety can also induce hormonal changes which can cause irregular periods. When the stress hormone cortisol is released by the body, it can have a direct effect on the levels of oestrogen and progesterone, which can change the timing of your menstrual cycle.
Irregular Periods in Girls and Women
Most young women get their first period (known as the ‘menarche’) between the ages of 10 and 15, but this varies between individuals. When you first start having periods, you may notice that your cycle is different each month for the first couple of years after menarche.
Girls going through puberty sometimes skip a period or get an extra bleed during their menstrual cycle. It is also not uncommon for periods during puberty to differ. While some periods may last for as few as a couple of days, other periods may be heavier and last for a week.
Sometimes a change in lifestyle, such as dealing with stress you may be experiencing, exercising more gently or eating a balanced diet may be all that’s needed to restore your normal menstrual cycle.
However, if your irregular periods become a problem or if you are experiencing additional symptoms see a doctor, who will be able to decide on the best course of treatment for you.
In many cases, irregular periods can be treated with hormonal medications such as oral contraceptives or an intrauterine device (IUD) that help to balance your hormone levels. source