Difference in tests

So the tests I took Tuesday and Wednesday seem to have a very faint second line, and the test this morning I *think* I see a second line but it almost appears lighter than the day before or two days prior? The first set of tests I used FRER and today’s test was FR Rapid Result and some generic from Target- I don’t know if the test used would impact the result early on. First picture is precious FRER tests and second picture is today’s rapid result/target.