Confused and could do with some advice

Ok so I took a pregnancy test yesterday and I got a very faint line but visible enough to be able to see it. However today nothing at all? I thought maybe it would be the same or darker but its completely gone. I'm still 2 days before my periods due so I'm not overly concerned yet but it's confused me as I've never even had a faint line before?
​Could it still be positive in a few days? Is it likely the original test was defective?