Actually it apparently IS possible to O twice in one cycle but it is quite rare.

Generally what happens is that for whatever reason, your body gears up to ovulate so you get all of the signs, but it stops short and doesn't pop the egg. This is quite common apparently. Unless you're actively ttc or trying NOT to conceive, most of the time you wouldn't even be overly aware of this happening.

I do agree that temping is about the only sure way to see if you have O'd or not. Even using OPK's is not a good way to be sure because you can also get positive OPK's and still stop short of actually ovulating. When you temp, the sustained thermal shift is the clearest sign of ovulation. Blood tests and/or ultrasounds are another method. And of course the BEST indication is a BFP.

Good luck.

Lisa