Could be your toothpaste. It also could be the regimen. The area around the mouth is sensitive to products and application of many things can lead to perioral dermatitis. I would stop using the benzoyl peroxide in that area and see if it improves in a week or so. If it doesn't, it could be either the moisturizer you use, or another product, or it could be some other skin condition.

its your run of the mill deep cyst that eventually comes to the surface, heals, and then the cycle starts over. I'll cut down on the BP, because ive been using MORE on the area trying to combat it.