Late AF or Pregnant?!

Glow has been very accurate in predicting my periods since I started using the app 4 months ago. It told me that the one for November should have started over a week ago. I took a Clear Blue test after it was 3 days late and it said Not Pregnant. The glow app had pushed my period back 4 days. It still hadn't started and after putting on my daily log that it hadn't started it was once again pushed back and is now supposed to start today.I took another Clear Blue test yesterday morning and it also said Not Pregnant. I am now hearing that the Clear Blue tests that have the Pregnant or Not Pregnant aren't very accurate.

Should I wait before testing again or use another brand? Glow says that AF should now start today but so far nothing!