Whys my belly button peircing sore?

so I got my belly button pierced roughly, 5-6 months ago & it's healed pretty nicely but occasionally I'll wake up & it feels very sore. Now, I have three piercings in each ear & I pierced my own nose & it turns out I have a tendency to pull my peircings out in my sleep & I've noticed I tug on it in my sleep. But I'll stay up all night sometimes & it'll still be sore & when I wriggle it, the bottom design will be stuck to the hole. Does anyone know why it's still sore?