Did O occur?

This is my second cycle since getting off the BC pill. My bbt spiked significantly on the 14th day after my period, and on the same day I observed significant EW CM. I thought for sure O occurred, but the next day my bbt dropped back to the range it was at before and I am now on day 17 and still having low bbts. Why would my temp spike with EW CM, but not remain high? What's going on in my body?