Pregnancy tests getting lighter at 7w3d?!

Let me start by saying I know it might seem crazy that I continue to take pregnancy tests, but I had a MMC at the end of May and I’m terrified that it’s going to happen again. I’ve been taking about 3 or 4 tests a week. Up until a few days ago, the test line was really dark. Today it seems lighter. Does anyone know why this happens? I don’t have a ton of pregnancy symptoms. They are faint and they come and go. It was the same with my last pregnancy and it ended badly. My husband called the OB last week for me because I was nervous and they said not to worry unless I have cramping or bleeding, but you don’t cramp and bleed when you have a MMC. My 8 week appointment is a week from tomorrow but they don’t do an ultrasound until the 12 week appointment. I’m very scared.

Test from this morning:

Test from the middle of last week: