Injury behind your left ear could cause a hematoma (localized collection of blood), abscess (localized collection of pus), muscle pull, injury to internal or middle ear
, contusion or nerve injury
. Is there a swelling behind the ear
? If there was a jerk to the neck because of the impact, it could also have caused injury to ligaments, muscles or intervertebral discs (discs between the vertebra).
Hope this helps. I think you should discuss this with your doctor and get your self examined.