Pregnancy tests not getting darker?

Rachel👨‍👩‍👧🤰🏻

Anyone have any experience with their pregnancy tests not getting darker? I had a mc in February and was blessed to get pregnant this month. I first took a test Monday (11 DPO) night and got a positive, although it was somewhat faint. I took another today (15 DPO) and while it is still showing a line, it hasn’t gotten darker and almost looks lighter. Has this happened to anyone? I’m thinking I’m going to have another mc :(