Sorry to hear about your frog. One of the problems that frog keepers face is how well these animals are kept by the pet shops. Most likely the frog was wild caught. They are known to have diseases or infections. The fact that some pet shop people do not know how to care for these animals, they often times suffer. Try to find a reputable breeder nearby or look in the ads for a reptile and amphibian breeders expo - they usually have a wide variety of animals for sale.