I have a few suggestions...
This will only help with making sure no other fluids are backing up in his ears...make sure he no longer tilts his head back to take a drink of anything, stop all bottles and sippy cups that he has to tilt his head back to get a drink from, stick to straws and straw sippy cups.
Also when bathing him put a little cotton in his ears to catch any water that may flow in. He will hate it at first but by the 2nd or third bath it won’t be an issue. Worst case cup your hand around his ear when rinsing him to block the water.
I don’t know if you have tried the antibiotic shots... when my son was 10 months old we tried it as a last ditch effort. He got 1 shot and honestly the next day he was no longer pulling on his ears and the crying stopped. Now I know a couple of other moms that have tried the shot rout and also had perfect luck, although one mom had to take her daughter in for 3 days straight to get the shots. My son only got one so I have to guess there are different shots out there.
That was my sons last ear infection, but personally I feel it was also a combination of stopping the head tilt to drink as well he was off the bottle 1 week before he was 11 months old, and like I said he has never had another ear infection again and he is now 18 months old. Some kids just have small ear canals and the smallest amount of trapped liquid can lead to an infection
Just a few things I tried...