I would be strongly tempted to get that bunny to a rabbit-specialist vet. If it is ear mites, that can lead to serious problem farther down the line, including head tilt. Your bunny may need a course of Invermectin....shots are more effective than oral medication. And yet you do have to get that ear cleaned out, this is nothing to ignore. Good luck!
see www.rabbit.org to find a rabbit-veteranarian in your area.