no lh surge???

i am in my fertile window and glow says tomorrow i have the highest % to get pregnant but i have been using opk since the start of my fertile window and always got negatives ??? I have been experiencing cramps (that ive never felt before) around both my left and right ovaries a bit before the start of the fertile window . Could i have missed my Ovulation? could it have happened very close to the end of my period? so confused thanks in avance for ur help ladies xxx