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I would ask you to get a scan of the abdomen which can give clue into any ovarian anomalies which can be expected in women of your age.A detailed follicular study
would be necessary here to ascertain that the ovum is been produced at right time in good health.
Also since you had a previous birth the cause for this delay now could be due to any structural defect left over by the previous child birth.Do consult a gynaecologist for the same.
Wish you good health