Late period

Last period was May 18-23, had sex June 13th and haven’t had my period since. Should I be concerned? It’s now July 2nd still haven’t gotten my period! I’ve taken 3 test. 2 test 1 week after missed period and 1 pregnancy test 2 weeks after my missed period. All showed to be negative! I’m just really confused, is this normal for a 19 year old to miss a whole month? Boyfriend 100% confident I’m fine. Which I believe him, just confused on why it would be so late. Please help.