My 6-month old Yorkie-poo has had a persistent cough when she wakes up since she was 3 1/2 months old. She has been checked by 2 different vets and been prescribed antibiotics 5 times. She has had all of her shots and seems perfectly healthy in all other ways. The only thing I have seen her do that is unusual is eat rabbit droppings in the backyard. Could she have allergies?