HELP!!!

my last "period" was on october 13th. there was only one time during those 4ish days where i had bright red blood and that was first thing in the morning and only once. the rest of the time it was really light and brown colored. i've had frequent headaches lately and been kinda stuffy. my period was due on thursday, it's now saturday, and nothing. i'm 17. could i possibly be pregnant?