Hiya,
Not exactly the same thing but I've been getting very similar OPKs since coming off bcp three weeks ago.
Sometime they lighten up and then go dark again, but I have had a run of over a week of 'positive in the next couple of days' lines but nothing changes.
I did read a bit about it and I think it can be your body gearing up to ovulate but there not being enough LH so it doesn't happen and so it will keep trying.
Sorry not much help but I did read OPKs like this usually happy after coming off birth control so I think it is just your body adjusting it's hormone levels.
You could of course be preggers as OPKs do start getting darker so it's probably worth doing a test if you have one handy!
Ed xxx