AF is confusing me... Any advice ??

My period was 5 days late, my back is killing me, my boobs are sore! ... When I finally got my period I was kinda bummed... But I noticed something very odd... Normally when I get my period I'm really really heavy flow (it's been like that since I was a kid) anyways but I noticed that there was only a spot on my underwear with some brown stuff. So I thought to myself "okay maybe throughout the day it will get heavier." But it's been 3 days and I don't even fill up my pad its only like a small little stain. Is this something I should be worried about? I'm mean my period is completely gone and it's never been like that! My period is normally 5 or 6 days this period was only 3!