First of all, you need to rule out pregnancy
completely by one blood test
for beta HCG.
Other reasons for irregular delayed period are hormonal
imbalance, ovarian cyst/ PCOD (most common), stress/ anxiety, thyroid problem, wt gain/ extreme loss, irregular eating habits, ovarian cyst etc.
Here, you need to consult with gynecologist for relevant investigation like USG abdomen and other hormone assay, blood sugar & prolactin
level etc. Proper treatments depend on causative factors. Hormonal medication is the key to regularize your period.
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.