3days late

My <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a> is usually right when it comes to me getting my periods, but now It says 3days late, I'm having cramps here and there and discharged I took a pregnancy test last night but nothing showed up it came out as invalid. And recommendations ?

Btw: we are trying to get pregnant.