It did the same thing to me last month!! Here's that chart.
http://www.fertilityfriend.com/home/23661b/rss3938.xml I'm still not sure exactly when I ovulated. I do think it was the original date (had EWCM & ovulation pain) and that I was going triphasic and possibly pg. I had one very BFP and my usual symptoms (queasiness, really bad gas pains, exhaustion), then many BFN but then AF came.

The good news is it looks like you're covered w/ BDing either way! Good luck!