The clear blue digital are very good especially ones with smiley faces,since you are only guessing when you ovulate, you may not be near yet,dont panic you will get the smiley face soon,as pp said dont pee for few hours.I used the same ones as yourself, i tested each day about 3pm, i also invested in cheapie ones from internet,and used them in the mornings,just so i didnt miss the surge.good luck.
I think i tested for a week and half before I got my +opk. Hang in there, Im sure it will happen soon...I found it was easyer to pee in a cup and then dip it in that. And are you holding your pee for a good 4hours before testing? and testing at about noon??