am I pregnant ?

SO my fiancé and I have been trying for a baby . We’ve been unsuccessful In the past so I looked into this app and have been following along with it. the app told us to “try” on the first . It was our highest chance of pregnancy or so this app told us lol. Well the app also said my period would come on the 13th ( if it was coming) which we obviously hoped it would not.its now the 18th and my period has not came . Should I begin to get anxious and get a test or wait ....?? Kinda lost ...