My one and a half year old shar pei/boxer/??? mix is itchy. I have him on Natural Balance Venison and Potato, which did help to decrease his itchies (as well as help with his loose stools), and I have gone on to add olive oil and the occasional egg yolk to his food, which has helped with his skin's dryness, but he continues to itch. He doesn't have any fleas and is on a flea preventative. His itching has definitely improved since switching foods two months ago (he used to chew scabs onto his rump), but he still itches a ridiculous amount. What could this be? How do I make it better?