It is important to consult a gynecologist in order to be certain that a more serious problem is not the cause, such as endometrial (uterine) or cervical cancer. Sometimes, something as simple as pregnancy could be the cause of these symptoms, and so it is always important to initially rule out pregnancy, by doing a simple free pregnancy test.
When estrogen and progesterone are out of balance during the different aspects of the monthly cycle, the effect is that the lining of the uterus is not all shed together and at the same time as is expected during a period. When that happens, the lining keeps building more and more on top of itself. Eventually, it gets so thick that it outgrows its own blood supply. Subsequently, with a lack of needed blood flow, the surface cells die off and shed. This die-off and shedding are seen as vaginal bleeding by the patient. Since it is not timed and predictable, this leads to concern and anxiety.