Help me figure this out

I am normally on a 28 day cycle with AF coming on the 11/12 every month for past few months that I've been tracking on Glo. Today is the 13th and already on 11/12 took hpt and got BFNs.
 When should I test again? Could I be pegnant but with low levels of HCG? What should I do? How long should I wait to test again? My AF is normally on time so this is super confusing especially with BFNs and I've never missed a period