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Menstrual blood flow and cycle duration varies in every woman and spotting or anything does not indicate infertility.If you have a regular 28 day cycle then ovulation chances are more between 9 to 16 day of cycle and first day of period is counted as day one.
Relax yourself as stress can delay the periods and have regular intercourse during ovulation days.
You can use Ovulation prediction kits.Have healthy balanced diet and drink lots of water.Avoid smoking and alcohol.
Take care!