On Saturday I have been hit on the mouth by a baseball and now my left ear is still ringing. I figure it would go away but it didn't. I plug my right ear and try to hear out of my left ear but I couldn't. It just sounded muffled.

You need to see a Physician.

But what could it be?

Damage to the nerves - that's a real possibility.

Ya but that the question. I already do have a hearing loss. I wear hearing aids. I have this rare condition that my nerves are dead. And I can't see a doctor till Monday