Again, I wasn't as far along as you, but I had a major amount of fertile CM for over a week before I actually O'd. It drove me crazy... and really wore out DH.
My OPKs were faint then started getting darker then got faint again and then were finally definitely positive... after I think 8 days of fertile CM (I usually only get 3-4). I also had incredibly pronounced O symptoms, very sore BBs the entire time, really moody, bloated, etc.
Your body is just trying to figure out what the heck is going on with the hormone fluctuations. Definitely keep using those OPKs because your surge just might come out of nowhere!
Sorry it's so annoying, though.