Opk question

Lindsay
So I just today read that you shouldn't use fmu for opk! Oops! I have been using fmu with the clearblue easy brand and got a positive one day only yesterday morning early. Then neg this morning. Can I assume I really surged Sunday and when I took my test early that morning the hormone just wanted strong enough to show up? Is it normal to only be positive one day? 
Just trying to make sure I planned my bd correctly. 😉