should i be concerned????

so my period was regular up until the 26th of october when i got an unexpected period. i took a plan b on the 19 of october so i don't know if that has anything to do with it but this will be the second time i get a unexpected period after exactly a week and 5 days. i'm going to the doctors tomorrow but do you guys think it's anything concerning??? (btw i went to the doctors on the 29th and got tested for stds and it was clean & i have the same partner every time and it's unprotected sex, planning on getting on birth control)