The first day of ur period have sex and if that doesn't work keep a Calender of ur period and do it two weeks before ur suppose to start and just keep trying.
There is an app called my days and plenty of others that help lay out your most fertil days and the day you're expected to ovlulate. Extremely helpful if you are unsure (: best of luck to you
It helps to go on prenatals when you start trying. Good luck :)