| I assume that you are not on any form of hormonal contraception. If that is so, and you are not pregnant, it may be that you have stopped ovulating and are having what is called dysfunctional uterine bleeding (DUB). DUB is very common. It is caused by hormonal imbalances which may be stimulated by excessive exercise, dieting, or stress.
Other causes of irregular bleeding that is not DUB include pregnancy, sexually transmitted infection, polyps on the cervix, and using certain forms of hormonal birth control — such as the pill or the shot, or cervical cancer. Because there are so many causes for the bleeding you describe, you must be evaluated by your health care provider.
The first thing to do is to take a pregnancy test to find out if you are pregnant. Whether or not you are pregnant, you should also visit your clinician. If the bleeding is related to unintended pregnancy, you will want advice about prenatal care or your other pregnancy option, abortion. If you are not pregnant, your clinician can help you determine the cause of the bleeding. Although irregular bleeding is common, you need to be sure to rule out any of the more serious possibilities. | 
