Plan B and late period

I had unprotected sex about a week and a half ago. I took the Plan B pill 2 days after.  I'm now 3 days late and my period is ALWAYS right on time.  Does the Plan B pill usually delay your period? I've never taken it before this so I don't know how that works.  I took a pregnancy test yesterday and it came back negative but I'm just curious if a delayed period is something normal.