late period

In breif. 3 days after my last period had sex and the condom broke. The next day I took plan b.(Saturday morning)  A few days after I took the plan b.(Wednesday) My back really hurt. The next day (Thursday) I started bleeding for a couple days. Now it's time for my next period and it's 6 days late. I just want to know how long I should wait till. Should I wait till next month to see if it comes or should I take a pregnancy test sooner? On the plan b box it said "next period may come early or late".