4 day late AF now spotting confused?

Vivian • God knows best
Ok so my AF was suppose to show up tuesday & it didnt i had no cramping or anything till today. Today is friday & i just started feeling menstrual cramps & light brown spotting.Last month i had a very short period that only last for 3 days i figured that was my implantation bleeding.But now im more confused then ever i dont know what to do at this point.