Ovulation test

My fertile window started Thursday. Friday I took my first ovulation test and I had two clear lines but they weren't quite the same color so I took it as negative. My ovulation day is supposed to be Monday but I took another test this morning and another after waiting 4 hours and both the lines are really faint. Shouldn't the lines be getting darker as i am getting closer to my ovulation time?? Any ideas why this happened?