What could be going on?

So for about a week or maybe a little less, I have taken a few pregnancy tests and the lines have all come back with a faint positive but they do not seem to be getting darker. Last month we had what was thought to have been a chemical pregnancy because the same day I got my faint positives I started bleeding, and clotting mildly. I have booked a doctors appointment but can’t get in until Sunday. What could it mean if I’m getting positives but they don’t seem to be getting darker? Also don’t seem to be getting lighter. All of these tests are different and from different boxes. They’re in order of days I took them over the past 3 days.

*To add all lines appeared at the 3 minute mark, the first test though I did take the picture a day after I took the test which is why it’s slightly yellow