First of all, you should undergo one home pregnancy test or blood test
for beta-HCG to confirm/ exclude pregnancy at the earliest.
In exclusion of pregnancy, reasons for irregular delayed period are ovarian cyst
, hormonal imbalance, stress/anxiety, thyroid problem, weight gain (that you have) / extreme loss, irregular eating habits, psychological factor etc.
Need to investigate properly to pin point the diagnosis 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.