Early Pregancy?

Annabelle
Hi there, TTC here. I've had one faint positive pregnancy test and 3 negatives this week. However I'm only a week post ovulation today. I just can't help myself when it comes to testing! 
However I have REALLY sore breasts. According to the conception calculator I would be 4 weeks today if I am pregnant.
Could I be pregnant and it just not be coming up on the tests yet? I'm using the cheapo early detection hospital style ones!
Thanks