Fifty percent of the total mass of the atmosphere is located in the lower 5.6 km (18,000 ft) of the troposphere. It is primarily composed of nitrogen (78%) and oxygen (21%) with only small concentrations of other trace gases.
Having irregular periods is very common. I see them in my practice all the time. The causes can range from something insignificant to something that requires treatment. For example, if you're a teen, your body's hormones can fluctuate and take some time until they find a balance.
Polycystic ovary syndrome (PCOS) and hypothyroidism are two common causes of irregular periods in women. In general, the goal of treatment is to restore the balance of hormones in the body. If you have PCOS, your doctor may recommend birth control pills or other hormones to trigger a period.