J.M.
I was 8 days late this summer and convinced that I was pregnant. I took multiple home tests and a blood test. All came back negative. The doctor told me to wait to take another test until I was 14 days late and then call them back if I didn't start and still got negative results because it could be the stress of taking so many tests that was causing the negatives. Well, on day 10 I started so it was just a strange cycle (and maybe the stress thing).
I don't know if that is overly helpful to you. You can always call your doctor and ask for a blood test. They are much more accurate than the home tests.