Spotty Period

The day I usually start my period it's horrible cramps and a heavy flow. I started on 6/5 with the cramps and a light flow. Every day since then (4 days) I've been getting lighter and lighter, like hadn't had but one tampon that had been around fully absorbed, that was of course day one. Can anyone point me in the direction of why I didn't have anything other than one side with anything on it. The side as in like the outer layer only. Kinda weird. Thanks on advance!