Pregnancy tests, what do you guys think?

alright im 11 dpo...I did a PT at about 3pm today at my school, I saw a faint line present, so i got my teacher to look to just make sure i wasnt seeing things and she saw it to...I went to the walk-in clinic after school so at about 530 is when they did a test there, and they told me it was Neg...I came home and did another one and once again i got a faint positive..why would i get faints an they said no??