period confusion on the pill

Ca

help please! i had sex about two weeks ago and now i've gotten my period about four days before the sugar/placebo pills row in my pack, and the blood is brown. yesterday (the first day) there was definitely some red blood but today its just brown. i'm having all my normal period symptoms like dull cramps, mood swings, and my usual uhh.. bathroom habits, so i dont think its just spotting or discharge. also its too much to be spotting/discharge. i'm so confused! I'm only 18 and I've only been on the pill for two months so I'm a total rookie here. Does anyone know what this could mean? Is this normal? Could I be pregnant?