You can use basal body thermometer, and take your temperature every day when you wake up, before even getting out of bed. Keeps a chart listing your temperature, which should remain relatively the same for most of the month. Knowing your ovulation especially if your periods are not regular is a little bit confusing. Cycles can range from 22 rights up to 36 – an average woman’s menstrual cycle is 28days. Once you know your ovulation date, as a rule, you are most fertile the day before, during and the day after.
When is my Ovulation Date? – http://answers.ask.com/Health/Other/when_is_my_ovulation_date