Understanding BBT

MW
Hello, new to Glow. I have been charting BBT and my normal is around 97.9. A couple days after OD my temp raised to 98.7.  Since the spike my BBT has been steadily declining -.20 each day. I've read that BBT stays high if you are pregnant, so if I'm seeing any sort of decline, does that mean it's probably not going to be a postive result this month? I also went to bed later than usual last night so perhaps not getting enough sleep could lower temperature? We only just started TTC. This is our 2nd month. Thanks for any positive vibes!