Reproductive aged women are naturally used to having periods every month. It is no wonder then that most women get anxious when their periods appear to stop for no apparent reason. In many cases, there is usually not much reason to worry as the cessation of the periods is usually transient and innocent. However, if the periods don't return within six months, the cause should always be determined and rectified.
If you miss a period and are sexually active, the first thing you must always not exclude is the possibility of being pregnant. This is regardless of being on contraception due to the known small failure rates even with the most effective contraceptives. If the pregnancy test is negative, the likelihood of some temporary disturbance of your hormone balance is usually the most likely explanation. There is usually no immediate reason to panic, waiting for one to two more cycles normally leads to spontaneous resumption of the periods. For some, the absence of periods may be due to a condition called Polycystic Ovarian Syndrome. There is usually a more pronounced hormonal imbalance, which results in the absence of periods for many months.