False pregnancy test?

I took three First Response tests and all three showed positive with faint lines indicating they were all positive tests! So I know one of the tests can't be defective. My friend is a sonographer and she scanned me last night - she saw nothing! She even gave me an ER pregnancy test and it was negative. AF was scheduled to arrive on 5/14 I had minor spotting (looked like old blood to me - brown colored instead of the bright red) for a few hours and it stopped. I haven't had it since! It's been i