Plan B after effects ?

So me and my so had unprotected sex 3 days before ovulation and he came inside me. 8 hours later we went to get a plan b! Ok so two weeks later I go to the bathroom and wipe and see red blood ( I'm not due on my period for another 8 days) so it was light I don't need pads only when I wipe ! Is this a side effect? I went to the bathroom to day and day it was on my underwear