Late(?)

<a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> predicted my period day for today, Tuesday the 9th, but I haven't started. I've been cramping for a few days, but just this morning I've been having straight up stomach pains and I feel kinda nauseous. Which begs the question, should I be worried? 
P.S. I'm not on any form of birth control.