Lines on OPKs

[Pickle0]

I understand that the line needs to be as dark as or darker than the control line for it to mean you are ovulating but....

I have been taking metformin for almost 3 weeks now have gone up one tablet each week and now on 3 a day, no sign of AF.

I have been taken OPKs at the same time most days and the line has been almost invisible, I would only see the faintest line when it was angled at a window with good light and I was squinting!!

But today, the line is darker, still very faint but I am not having to make an effort to see it. Does this mean that it will gradually get darker and darker every day until I ovulate?