When my yorkie Chewy was a puppy his ears flopped down. Someone told me its because they are teathing or the hair on their ears are to heavy and if they are still puppies you can tape them up for a few weeks until they are strong enough. I did it with Chewy and his ears stand up now. Sometimes when the hair on the right side gets heavy, his ear will flop over. It's not painful for them, probably just a little annoying. Try this website.
Top Taping Yorkie Ears Taping Yorkshire Terrier Ears Stand Erect Yorkie Ears