Amanda,
The only SURE way to tell if you have O'd is either charting or going to the doc for bloodwork and/or ultrasound. EWCM can give you a clue: The first day of dry up is usually (and please note I say USUALLY) the day of O. But you can have EWCM and not actually O. So you might see it again later if your body should try to O again. What I tell most ladies when they see this is to get busy again, just in case.
Unfortunately, there is simply no way to know for sure if you have O'd except by charting (well, that's the cheap way; u/s and bw can be quite costly if you intend to run in and do them every month!

)
Sorry I couldn't be of more help.
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You may have to fight a battle more than once to win it. - Margaret Thatcher
Ummm........yeah...sure...I've been good.