OPK- please give me ur advice!

Hi, I've been taking opk since Cd10, I haven't got a + yet. It's only cd15 but. I've tested 2x a day, with first response. My bbt chart says I o'd yesterday..? Anyone else know they o'd even if they didn't get a +..?? I usually get them but the last 2 months I haven't. I've had bloods done a few times also n progesterone levels show that I o'd... What's everyone's progesterone levels...?