Pill not working ???

Hey girls, I'm on the Diane 35 pill, also known as Estelle, Laila or Chelsea 35, and the past few months my period hasn't been starting until the sixth day of the placebo sugar pills? It use to always start on the Monday when it's supposed to on the packet but now it doesn't start til Thursday afternoon. Is this normal? Does anyone know if this means my body is no longer responding to this pill?