OPK help?

This is my first cycle TTC and I need a little help! I've used these opk's everday so far of my fertle period (according to glo) and haven't had any even faint lines showing up? most of the posts I've seen of opk's the test line is there, and just gets darker each test as you get closer to ovulation. Im on day 14 in my cycle and still no test line? Do you think thus means i just ovulate late than glo predicts, so I have a longer cycle. Or maybe these cheap tests don't work?