I have a wonderful rescue dog, a cairn/jack russell/schnauzer mix. He's a real sweetie who rarely leaves my side, (this does of course, mean that he gets to lie on my bed or sit in my recliner with me). The last few weeks he has been constantly scratching himself, biting at his skin, and licking. I know his flea treatment is up to date, and I have even gone through his fur carefully looking for any survivors, and haven't found anything. Could he be having allergies?