It's really hard to say, everyone is unique. Some women do see a temp drop right before O, but not everyone, so even though it's common, you *may* not get one. I would say, though, if your temp is lower all of a sudden one day, make sure you get dtd!

Once O has actually happened, your temp will rise and stay up, and then you will know it has happened. They're looking for three temps that are consistenly higher than your previous six temps.. and that stay there.
GL! It's actually a really exciting thing to watch! lol