Pregnancy test changing?

Okay so. Last week when my period was 7 days late I took a test. Clearly a negative. No slight lines, not even the faintest. I took another one this morning (12 days late and used morning urine) it again was a clear negative. Not even hinting towards a positive. I was looking at my first test and now I don’t know if I’m seeing things but I swear there’s a SLIGHTEST hint of a line. Can a pregnancy test be accurate after almost a week of me using it? Can it change from negative to positive even though my most recent one is a definite negative? I used first response if that helps. Also. When looking at it under direct light it kinda seems like it’s just an indication on where a line would show up, not really a pink colour or anything. Just super super faint, almost barely noticeable unless held under direct bright light. Could that be it? Or could it be a positive now after a few days of sitting?