But if it's always been tried and true, my first thought would be that you have delayed ovulation
. And it's most likely because you're trying to coneive, and are stressed out and nervous thinking a lot about it, and this can most certainly delay ovulation. Try having a nice glass of wine unless you are way against drinking, and try to not think about it. I did this, before I ovulated, was so afraid I wasn't going to, and low and behold, the next morning I got a positive OPK.