I’ve had a chemical before, and I’m sorry to say, but I think you should prepare yourself for that as I think from Saturday to today you should see more progression. To add though, you shouldn’t compare different brands, and your last tests seems to be slightly darker vs the first one, so could also be just slow progression. These strip tests are notoriously slow to get darker.
Mine was lighter than the first one at 14dpo I almost threw it away thinking it was negative. I now have a 15 month old baby girl. So hopefully all is well with you x