There are several reasons of delayed period and these include ovarian cyst
imbalance, uterine pathology, stress/anxiety, thyroid problem, wt gain/ extreme loss, irregular eating habits etc.
But, first of all, you have to rule out pregnancy
by doing one home pregnancy test initially and one blood test
for beta HCG to confirm the same.
In exclusion of pregnancy, you need to consult with gynecologist for relevant investigation like USG abdomen and other hormone assay etc. Proper treatments depend on causative factors.
Avoid stress by regular deep breathing, take healthy diet with Vitamin & iron supplements
, control body wt and need proper sleeping.