My 9 mos old Shih Tzu is scratching terribly. She is current on Advantage, no visible fleas, bathed in Oatmeal Shampoo with Relieve for itching. Can I give her Benedryl? how much? is something better? I started her on 1/4 tab of Tums twice a day for eye stains, is it likely that this is a reaction to that?