False Negatives

How common are "false" negatives when taking a HPT before your missed period?  Has anyone every experienced this and were truly pregnant? 
AF is due in 3 days and I took a HPT this afternoon that came back negative. I have been running to the bathroom all day (seriously it's like someone forgot to turn off the faucet) my boobs hurt and have a stabbing/tingling sensation in my nipples, my back hurts and Im bloated like a bullfrog.  
Really hoping that I still have a chance and that I just tested too early.