First photo is 12DPO second is 15DPO. I’m starting to get worried, I feel like it should be getting darker by now. Anyone else have this happen and it eventually get darker?

Edit:

First is not FMU Second test is FMU

Update:

20DPO and my line is SOLID. Top picture is 20DPO. Thank you for all the supportive messages! Just wanted to share for any one who may be as anxious as I was.