Why is only ONE of my Dog's ear always dirty, stinky and red?

Question by Matt W: Why is only ONE of my Dog's ear always dirty, stinky and red?
I have a Pug that is about 15 months old. About 5 days ago I noticed that it's left ear was super dirty with dark crusty stuff, almost scabby looking. There was lots of wax buildup as well. The outer part of the inner ear looks red and a bit swollen. It also kinda stinks. I've been cleaning it twice a day and it's still really dirty each time.
The other ear looks perfectly normal. I don't think it's

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