OPK and ovulation help!

I need to pick some brains here! I had a positive OPK on Tuesday, or what looked like positive. We've been BD Monday through yesterday and plan on it again tonight. My BBT temp yesterday and today has still been low. Yesterday I tested again with OPK just out of curiosity and it was negative. However, when I took one today it was a full blown positive! Even darker than Tuesday. And I do feel kind of crampy (there is activity going on down there). So my question is this, is it possible that I am actually ovulating today? Or was I gearing up to ovulate yesterday and just didn't?