Should I just keep taking HPTs??

Mandolin
Ive tested myself for pregnancy 4 times in the last week or two. 
-5 days late: negative 
-12 days late: 2 negative tests
-13 days late: negative
My period is almost two weeks late, and I had unprotected sex twice early this month. Should I just keep taking them?? It could be too early and my HCG levels could be too low to detect.