Why Would OPK Be + 1-2 Days But Go Back to Being + ??? Anyone?

[carleeriver]

All have been light or no line then Wed + (darker than any of the previous days anyway) in PM (I do twice a day) and Thurs + in PM then back to light again. Now, last PM the line got a slightly more dark again and now this morning it's probably 2/3 the darkness of the control line.

What the heck?

 

[Feelcrazy]

Mmmm could you be preg?
I know they go dark when your preg ??