OPK testing - New TTC

Hillary
I am new to TTC and recently off of birth control after about 10 years. Glow predicted that last week would be my most fertile days and I have been testing with Clinical Guard OPK strips so that I do not miss my peak days. I have yet to get a positive. Anyone else in the same boat? 
Does an OPK positive have to be very dark double lines? Thanks in advance.