Hello, With missed Depo shot, there is quite chance of being pregnant. Here, you need to undergo blood test for beta-HCG and TVS scan to rule out conception at the earliest. Other reasons are hormonal imbalance, mental stress, irregular diet habit, wt gain or loss etc. Please consult with gynecologist after initial test reports to proceed other relevant investigations. Take suggestive measures accordingly. Maintain genital hygiene. Control body wt and avoid stress. Use regular contraception. Good luck.