Hi!
It is quite common for women to have an "odd" cycle now and then. Even women who are clockwork regular may have an occassional month in which the ovaries "miss fire" or fire a "dud". If for some reason ovulation is "off" the next period will be too.
I ALWAYS recommend a repeat test--I usually say weekly until the period starts or until positive.
Another possibility is to have a blood test done at your doctor's office. Your doctor could also possibly prescribe some progesterone for you to start your period for you.
Good luck!
Dr B
most pregnacy test are able to detect a pregancy up to 4 days early..if you are 7 days late and the results are negitive it most likly is..you could just be going through some stress in your life and that could be the cause...you should see your doctor and get a blood test thats the only way to find out for sure..my sister had a negitive pee test at her doctors office so you cant be sure untill you get the blood test