Always read the pregnancy test within the time fram given on the box. What you could have been seeing after that time frame are known as evap. lines.

it's possible your HcG (sp?) levels were not high enough on the first one. It's more likely to get a false negative than a false positive.

^^ as stated above, be sure to follow the directions precisely if you want accurate results.

evap line

I would take it again just to be sure. I had a false negative the first time I tested. We saw it again a few hours later when we were throwing it away outside and it said postive. So I tested again a few days later and sure enough I was pregnant. So yeah it's probably just from sitting for a couple days but test again to ease your own mind