After af when the body starts producing estrogen, which lowers temps, and stops producing progesterone, which raises temps, BBT is low and stays low as long as the body is not producing progesterine. On the day of ovulation, some women see a temp drop. I'm not sure what causes this temp drop. After ovulation, the body produces progesterone causing a temp rise of about 0.5 degrees F and stay high until af. If a fertilized egg implants in the uteris, some women experience a small temporary drop in temp due to a surge in estrogen. After the fertilized egg implants, it starts producing HcG, which, for some women, will push temps up higher. If a fertilized egg does not implant or for women who do not get the implantation dip or second rise, temp will stay at about the same level until about af or throughout pregnancy.

The temp change with af varies. For me, my temp gets erratic before af but doesn't really drop until the end of af. Some women get the temp drop just before or after af. Typically, progesterone drops before af but is still high until after af. You need to temp for a few months before you know what is normal for you.

Thank you VERY much shortgeek, I have been trying to understand it with no such luck.