Get thee to the vet.
Yeh, a vet. The flop-eared dogs can have terrible ear infections. My Border Collie had a lingering one. The vet kept giving him some goopy medicine. It did not clear up until another vet who really knew what he was doing treated it with yet a different medicine. It was already goopy/ no need for more.
It was a while ago, do not remember the meeds, but they can go deaf if it is not treated.