What to think?

So my <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a> said I was suppose to get my period on dec 22, but I still haven't received it. I did a test on Sunday dec 21, which was negative. So today dec 27, I did a test again today and still negative. What am I suppose to think or do now! I've been TTC since last year july 2013. Should I still wait and test on Monday? This is so frustrating. I've been eating my prenatal vitamins everyday.