False Negative Pregnancy Test?

I was wondering if any of you ever had a pregnancy test be negative but you actually turned out to be pregnant? I am a week late, and I normally have a pretty regular cycle, but I have taken tests and they are negative. My doctor is having me do a blood test, but I won't know the results until Tuesday! I was just wondering if this has happened to anyone? We are trying to conceive so I am trying not to get my hopes up, but that's easier said than done.