Questions about one's menstrual cycle are best answered by an obstetrician-gynecologist. Overall, the hormonal regulation of the menstrual cycle is quite complex, involving two parts of the brain, the hypothalamus and the pituitary gland, as well as the ovaries and uterus. Pregnancy results in a (perfectly normal) disruption of the signaling cascade that leads to regular, monthly menstrual cycles. It is not unusual for it to take several months for this cycle to return to your pre-pregnancy baseline, but it can be very frustrating to have such irregular periods.
In general, it is best to have sustained, irregular periods evaluated by your gynecologist because he or she can do a more detailed history and physical examination, as well as some laboratory testing if indicated, to make sure that there are not signs of any other hormonal or endocrine causes for irregular periods. Thyroid disorders, for example, can cause irregular menstrual cycles. However, if there are no signs or symptoms of any other issues, the easiest way to regulate one's menstrual cycle is to use oral contraceptives. Even if such medications are not specifically being used for contraception
they do have the side effect of leading to predictable periods. Not all women wish to take OCPs and this decision is best made after a discussion with you and your physician. However, if you and your doctor
decide this is a good option for you, OCPs will lead to very regular cycles.