Peak Smiley - No bbt rise ??

Erin

Last month I started temping and got a big jump of .4 c and I presumed that was ovulation. This month I used opk kits too. On Thursday I got a peak smiley. Had sex the wed/thur/fri just to be sure. But today (Sat) I got up and took my temp again and it's still low however my opk are now negative. Any ideas?? Has this happened to anyone else?