HELP! Emergency contraceptive PANIC

Last month, shortly after my last period, I had unprotected sex with someone.

Did not take a pill

A week back, just before my period was due I had sex with a guy and the condom slipped out. The next day (day my period was due) I took a pill.

My period is now 4 days late.. How concerned should I be and when should I take a pregnancy test?