Use an app or a regular calendar to track your period. Note the time from the first day of your period to the first day of your next period, and you will get an idea about your cycle length. And once you have that number, subtract 14, and you will roughly get the window when ovulation would occur. For instance, if your cycles are 30 days from one to the other, 30 minus 14 would be 16, so ovulation would be on day 16 of the cycle.