Ovulation Confusion

MommaBrew • Jesus Loving, Homeschooling, Hubby obsessing, Beautiful kid making Superhero
HELP! I have been testing for ovulation for the past 8 days and I have NEVER gotten a test line as dark as the control line. What could be going on?  
My last cycle was March 21st and I am suppose to start another cycle according to Glow on April 16th. We aren't really trying to get pregnant but we aren't being careful either (no birth control at all). 
I have been told that as long as a line is there I am fertile but at what point do I ovulate?!