I had unprotected sex a little over 2 weeks ago and am now 4 days late. I found an old pregnancy tast (expired in 2014) but thought I would do it anyway until I can get another one. I left it for five minutes and it was just showing negative so threw it away but looked again earlier and another faint line had apppeared indicating a positive result. Was just curious what the chances of it being a false positive were?