Early Period

on August 23 i got my period after my cycle ended i did have sex I am suppose to get my period on September 20 but my period came September 18th but my periods never come early like this first i spotted then alittle blood came it dnt feel like my normal periods its much more lighter and not a heavy flow the flow is so light that i dnt have to change my pad i can keep one pad on all day what can this mean I am so confussed