hi ! if this is the first time you have missed your period, pls wait for sometime my be couple of weeks and if no period go for USG ABDOMEN,
THYROID PROFILE, fibroids or cysts or thyroid may cause such ups and downs in your periods. if the usg and thyroid are negative, then observe for any new symptoms that you might be facing, like hot flashes, heat much in the body, frequent sweats, etc,etc, then it might be menopausal stage, which you can get confirmed after consulting gyncaecologist.