With my first I bought a really cheap one from the Dollar Store, and it was...you guessed it...a buck plus tax. I took it and it was negative. So I played some hardcore volleyball, and then a couple days later, I retested with a more expensive brand and it was instantly positive. So when I went to the doc she said I was about 6 weeks, so I would've been about 5 weeks along, so it should've shown up. Well I ended up miscarrying. Whether or not it was due to the volleyball playing, I don't know, but I don't trust cheap pregnancy tests!