First of all, you undergo one blood test
for beta-HCG to confirm/ exclude pregnancy at the earliest. Early pregnancy test may give negative result.
Reasons for delayed period are ovarian cyst
or PCOD (most common in your case), hormonal imbalance, stress/anxiety, thyroid problem, wt gain (that you have) / extreme loss, irregular eating habits etc.
Need to investigate properly to rule out underlying pathology by USG lower abdomen & complete hormone assay, thyroid profile, blood sugar & prolactin level, blood testosterone level
etc. Consult with your gynecologist for proper guidance and take suggestive measures.
Avoid stress/ tension, take healthy diet with Vitamin & iron supplements
, control body wt by regular physical exercise and take sound sleep. You may need to take hormonal therapy to regularize period with other supportive medication
Be well and take care.