Lighter test line at 7 weeka

So i must like the torture..7w 3d ans i for some ungodly reason i tested again, the line is lightsr than it was when i initially tested and the mayne a tad lighter than when i tested thursday or friday. No bleeding and just occassional super light crampig ans still having my symptoms come and go like ive had. At 5w my hcg was 18,522 am i just over analyzing this? I heard that sometimes the more hcg u have the lighter the test line can be (hook effect)