Positive or negative?

Paola
took a pregnancy test and the directions said that I would get my results after 2 minutes, but it also said not to read the results after 10 minutes. After the 2 minutes it showed a negative result, but when I was cleaning the bathroom and when I emptied the trash I noticed the pregnancy test showed a positive result. So I was just wondering why they tell you NOT to read the test results after 10 minutes. And could I be pregnant even though the test first showed a negative result?