Dog seems to have lost control of one ear and shaking its head constantly?

My 6 month old papillon seem to have all of a sudden lost control of one of its ear. its just hanging there like its loose. Also she shakes her head constantly like she's trying to get it back upright and erected but can't. She does scratch the ear sometimes. I have another dog and its a yorkie and they do fight sometimes. could it be that they had a little rough fight and injured it or maybe an ear infection or could it be something even worst? Thanks in advance.