3 day period

So on the 13th i got my period on the day it was normally going to come but it wasnt as heavy as usal and i had some cramps but they werent bad like other times the next day it wasnt that heavy eaither and i had no cramps 3rd day it completely stopped i didnt bleed the entire day at all. & today i just started spotting again and its just little drops of light blood and out of no where it comes its not a flow or anything. My periods last atleast 5 days and the first 3 days are usally when i have a heavy flow. Do you guys know what might be happening?