My Dog Keeps Shaking His Body And Attempting To Scratch The Left Side Of His Head With Anything He Can Find. What Could It Be?

Yesterday when we arrived home from work we noticed our dog had a swollen eye. We took him to the vet and she told us to give him some benadryl and watch him to see if it got worse or better. Well the swelling is gone but now when he is standing up constantly shakes his body as if he just got out of a bath. Also when he' snot shaking he tries to rub the left side of his face on rugs, walls, and us. Left ear is floppy and somewhat sensitive now as well.