Late?

According to glow I’m about 3-4 days late. I am usually right on with AF & the <a href="https://play.google.com/store/apps/details?id=com.glow.android">Glow app</a>. I took a test today and came up negative. Has this happened to anyone? When should I retest? I don’t feel any symptoms of AF which I normally have sore breasts right before she comes. Any advice is welcome.