Hcg 6672 at 4-5 weeks pregnant, PLEASE HELP ME!?

Okay so this one is tough. And please, respectfully dont say, "honey you are pregnant." I do know I am pregnant but I am concerned about this failing. So here is what happened. I am a fertility patient, conceived my son with injectibles and now I just got pregnant with this one on my own. BIG SHOCK! So anyway, I took a test last Tuesday and the line was there are not light. Now I took one yesterday and the line was more faint and with the first mornings urine. Yesterday I went to the E.R. for dizziness and they did a Beta HCG and it was 6672. This is in normal range. So why the more faint lines? Is this pregnancy failing? I dont understand! I know if my HCG is 6672 then I should have enough in my system to show a darker line than what is being shown. It is first response coincidentally, which is what I used when I found out with my son. And by the way, I dont have any symptoms besides extreme dizziness and extreme fatigue.