panicking!!!

I Had Unprotected Sex For The First Time On Saturday And I Have Not Yet Taken Plan B .. My Breast Are Starting To Feel Very Tender BUT I'm also supposed to start my period on Friday?! Could I Be Pregnant Or Am I Over thinking this ?! 
Should I go buy Plan B ASAP Tomorrow or wait till Friday to see if I get my period?!!! 
Idk what to do! 😭😐