Help with OPK

My husband and I are TTC, I bought clear blue easy read digital, I have been testing 2x's a day everyday during my fertile window according to glow...have not gotten a positive LH surge reading at all. This is my first time using these, not sure how likely it is that I just tested at the wrong times and missed my surge? I'm pretty sure I am ovulating since I have always had ovulation cramping and CM Changes every month. Any advice?