Becca,
I'm new at this OPK stuff too. I test with urine around noon time (so it's definitely not first morning). I know everyone swears and tests differently with different times of day for urine.
I'd just keep testing with the OPK's. I think the line just pops and is suddenly dark when you catch a positive.
It's so tricky! I went ahead a bought a clearblue easy fertility monitor which I'm going to use in conjunction with my OPK's next month, if I don't catch it this month
Good luck.