Dip in BBT for one day? Have you had that?

Amber • 7/1/09 miscarriage (8w2d), 5/31/10 my son was born, 5/26/15 chemical, 6/24/15 chemical.
I've been reading up on it, and apparently it can be an early pregnancy sign? But not always. I did have a doc appt today, and they tested me but said it was negative. It was a urine test. I've not tested at home, and AF is due in 4 days. Have you had this happen? What's your experience with it?