Pregnancy Test Help!

I have had 3 apps for the past 3 years including this one that calculates my periods etc. I have recently been placed on letrozole this month. All apps have my period date on all different dates so I am unsure when I should take a pregnancy test. I am experiencing nausea, cramping, tender breasts and drowsiness. One app indicates I have a missed period by 4 days and the other 2 indicate I am not starting at all this month. Any advise on when to take a test?? I took one prior to my indicated period starting date for one app and had another negative test so unsure when I should take another test. Or if these symptoms seem like early signs of pregnancy?