What causes a test do be invalid after the time window? To begin with I seen nothing, after the time window I'm seeing a faint line. Obviously will test ina few days, but wondering if someone can educate me in the mean time! The first test in the time window was two lines, the control and one after the control, figured faulty test, I waited 5 days, took another. Appeared negative, looked later and see two lines with the test line being faint. So now I'm waiting another few days to try again. Wondering if it's because tests are the cheapy ones