Super frustrated

So I am now 8 days late and have peed on 3 sticks yesterday morning I swear I saw a faint line and then it disappeared. It was a first response test and I've been reading that it happens. I took a clear blue test and it said negative. But I am never this late. If I am prego I would be five weeks and I'm super crampy. Has this ever happened to anyone else and it turned out they were  pregnant? I'm going to try and get in with my doctor on Monday.