False Negative Test??

Hello! just curious if anyone on here has ever had any false negative tests and it turned out you were actually pregnant. I've been having cramps on and off for 2 weeks now. I thought it might be my period but it wasn't. My last period was on 1/23/18 and it usually lasts 4 to 5 days. Last time my SO and I had sex was on 2/20 and I was expecting my period around the 23 to 25th of February and up until today no period yet. I have been feeling off lately. I am feeling and nauseous easily, having really bad heartburn to the point I wake up in the middle of the night and the cramping. Usually when I get cramps I get my period the same day or within 24 hours. I have tested 3 times and all have been negative so I am curious as to how many of you have had false negatives and when and how did you confirm you were pregnant. Thanks!