OPK help please!

Okay. So I took 2 OPKs this morning. One when I first woke up, and one around 11. The line got lighter around lunch. But someone told me to take one in the afternoon. So I just took one and the now there isn't a line.
 So, at 8 the line was dark (but not quite as dark as the control line) 
At 11 it was a little lighter. 
Now at 1:45 there's no line. 
What could this mean?