You can almost count on it being a yeast infection. Yeah - it took a vet visit, unless you're a regular customer with a chronic, and you need refills. My Logan lab was a chronic, got infections if he swam in any kind of fresh water, I took to only swimming him in salt water after awhile.
There is a home ear cleaning remedy vinegar and water, but if he's already infected that will hurt and he'll fight it. I also think it makes him smell like a salad, but some hunters recommend using that after they've been in water to prevent infections. It won't cure one.
I'd see if you can get in. He'll be 90% better after the initial cleaning and treatment, then you follow up with the antifungal for a few more days. But if you let it go, they can end up with a secondary bacterial infection too.
Thanks for the info. I will have to call the vet then. I ran out of the ear stuff, I had for my other lab. Her ears were worst, because I swam her more. I sure hope you find out what is wrong with pony.