Suggest Remedy For Delay In Periods

Hello I am 19 and I missed my period...it is supposed to come May 6th but its been 3 days. I took 4 HPT, and all came out to be negative. Me and my bf used the pull out method.. my last period was on April 6th, we had unprotected sex a week on a Monday (which was April 12th)...Two - 3 weeks passed and I still dont feel any kind of symptoms relating to pregnancy...does this mean I am not pregnant?