First of all, you need to exclude possible conception by home pregnancy
test or blood test
for beta-hCG if you are sexually active.
There are several reasons of missed period like hormonal imbalance, stress/ anxiety, ovarian cyst/PCOD, thyroid problem, wt gain/extreme loss, irregular eating habits etc.
Need to investigate properly to rule out underlying pathology by USG lower abdomen, Thyroid profile, LH/FSH etc. So consult with your doctor and take suggestive measures.
Take low carbohydrate
foods, reduce body wt and avoid stress by regular meditation
or yoga. Hormonal medication may be needed in the absence of pregnancy to resume period.