First of all, if you are sexually active, then you need to rule out pregnancy
by doing one home pregnancy test initially and one blood test
for beta HCG to confirm the same.
Other reasons for delayed period are hormonal
imbalance (most common in your case), stress/ anxiety, thyroid problem, weight gain, irregular eating habits, ovarian cyst
Here, you need to consult with gynecologist for relevant investigation like USG abdomen and other hormone assay etc. Proper treatments depend on causative factors.
Do these things- Avoid stress/ tension by regular deep breathing, take healthy diet with Vitamin & iron supplements
, eat more vegetables & fruits, drink more water, keep bowel habit regular, control body wt and need proper sleeping.
Be well & take care.