Took a opk yesterday morning and got positive. Took one last night and this afternoon and got negative. Using digital so it's pretty accurate. Is that odd for a positive just to show up for a day and then be gone by that night ? Also yesterday was cycle day 16 when I got the Positive. Am I ovulating now ? Cd 17 or did I yesterday ? Confused about the test and how to determine exactly when I ovulate based off of it. Thanks !