5 Days Late, negative pregnancy test. Help!!!

Crystal
I'm five days late and I tested negative on the pregnancy test. A little background history, with my daughter (only kid) I didn't get symptoms until I was 3 1/2 months. I tested on a hpt and it was positive. Took a blood test came back that I was 6 wks. When I went in for my ultrasound I was really 3 1/2 months! Any thoughts?