Hello, 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.