Possible False-Negative Pregnancy Tests?

Ok, so the last time I had was the middle of January (I can't remember the exact date.) I had my period the begining of Jan, and it was normal. Aunt Flo is always the same..first week of the month, Niagra Falls lol, and lasts about 5 days. February I had a very light period it was almost non existent, and barely lasted 2 days. Now I'm just over 2 weeks late. I have been so extremely tired, I've noticed some tenderness, as well as bigger and darker and I've been experiencing dizziness. I haven't been experiencing morning sickness. I've taken 4 home pregnancy tests, and they are all negative. Is it possible they could be false-negatives, even this long after possible conception? Or am I just worrying over nothing? lol Going crazy here!