I don't know what's going on

Hi guys so I'm a little confused I had sex back in may and to be safe I took a plan B a few hours after having sex. I was supposed to get my period June 7th. June 7th happened to be the day I had to get tonsil surgery and with every surgery they do a pregnancy test and mine was negative but here I am 3 weeks later and still haven't gotten my period. I took 2 pregnancy test today and both were negative. It's been 6 weeks now since we had sex so if I'm pregnant shouldn't my tests show positive and if I'm not pregnant shouldn't I have gotten my period by now??????