What could it possibly be?

Ashley

I was 3 days late for my period according to glow, and I got it out of no where, it was mainly bright red and a little bit of darker blood here and there. Last night which would have been the 3rd day of having my period I didn’t bleed at all, and today it had been so light like it’s about to end? I still have 4 more days on my period, any ideas??