Shih-tzu from Puppy Mill

I bought a 4 month old Shih-tzu puppy from Pet Palace in July, assuming it would be in good health. After doing research on the breeder I have come to find that he has had numerous investigations of puppy mills. When I called the pet store they had no sympathy. My dog has kennel cough and has sever allergies to everything. I am very distraught and upset with the situation.