Hello, Thank you for your query. I believe, based on your symptoms, it could due to an ovarian cyst. This is mostly a harmless condition in which, the follicle that contains the egg or has released the egg becomes filled with fluid. This causes hormonal imbalance which delays your ovulation & hence your period. This functional cyst mostly resolves itself without treatment in 2-3 menstrual cycles. Occasionally, it is big enough to warrant close observation, medication and rarely surgical intervention (to remove that cyst that can twist or rupture and cause life threatening consequences- torsion) Let s wait for the ultrasound to see if there is a cyst and what s going on. However, other factors like stress, illness, travel across time zones, sudden weight changes and major lifestyle changes can also can delay ovulation and periods. If this occurs frequently, you will need to check for thyroid hormone imbalances and prolactin levels. Maintain a healthy lifestyle /diet and a regular sleep pattern. Stay well hydrated. Hope this helps. Please let me know if there is anything else I can help you with. Wish you good health