I have missed my period for 4 months and have gone for ultural sound scan and pregnancy test but all the test says its negative but i'm very worried ?

Anovulation: If all your tests have been negative and the ultrasound is fine, it is possible that you are not ovulating. Ovulation sets a biological alarm clock that causes a period about 14 days later. If you are not ovulating, then you won't have a regular period. Eventually, you may begin to have heavy, irregular bleeding. You may want to be on a birth control to help your body have a regular period.