As menstrual period occurs on 14th day of ovulation, irregular periods
means irregular ovulation.
As you are obese
& not getting periods for three months, might be suffering with Polycystic ovarian cyst
might be required.
As you are young, should be optimistic.
With treatment you can perform one mala daily of "Devkisut Govind Vasudev Jagtpate, dehi me tanayam krishanh, twamaham saranm gath".
With good wishes,