If you have a shorter cycle, mine being around 23 days, is it possible that you could measure slightly ahead? I had noticeable symptoms at 3 weeks and 1 day and my first positive results at 3 weeks 4 days. By 4 weeks the line was very dark and I was exhausted all of the time. Just wondered where I am 5 weeks today (last period/withdrawal bleed from the pill was on 25th May) or perhaps slightly further along?