First of all, you have to rule out pregnancy
( as your period is late by 3 weeks from expected due date) by blood test
for beta HCG or ultrasound
In exclusion of pregnancy, causes of irregular period are hormonal imbalance, stress/anxiety, ovarian cyst/PCOD, thyroid problem, wt gain/extreme loss, irregular eating habits, psychological factor etc.
Need to investigate properly to rule out underlying pathology by USG lower abdomen,Thyroid profile, LH/FSH, blood sugar, blood estrogen & progesterone
level etc. So consult with your doctor and take suggestive measures.
Avoid stress, take healthy diet with iron supplements
, control body wt ,maintain genital hygiene and need proper sleep.
For direct consultation with me, you may visit my profile on http://www.healthcaremagic.com/doctors/dr-soumen-patra/63326.
Be well & take care.