My Mini Schnauzer has extremely dry itchy skin. I give him olive oil in his food 2 - 3 times a week which has seemed to help, until the fleas started showing up. The vet gave me Frontline, knowing his skin condition. I was hesitant, but used it, now his skin is worse. Much worse! Dry, flaking and visibly red and places. Without going back to the vet and paying another $75 for an office visit, can I give him Benedryl liquid? If so, does anyone know the safe amount for a 13 dog?