Understanding BBT

I'm trying to understand my BBT.  Normally when I wake up I'm consistently 97. something, yesterday (Sunday) morning when I woke up I spiked to 98. something (I had like a .47 degree spike) but then this morning (Monday) I dropped like 1.13 degrees? When did I ovulate?? Before the spike, during the spike or after when I dropped? When should we have had sex?