Dog had black goop in ear(1 ear only). Thought it was mites. Been treating with nustock stock for about a month. I gave a small break after the first 3 or 4 doses and the black goop came back been treating every 3 to 4 days since then and he still act like his ears are bothering him. Possibly a yeast infection or what else could it be? If it is a yeast infection would monostat cream work?