He hasn't had 4 food changes in the last 8 months. I guess I worded that wrong. He's been on 4 foods in the 13 months that he's been on solid food. The Iams puppy was the first 2 months, I switched to Blue and he was on that doing great for several months then out of nowhere the softer stuff started to come out. I think it was in the middle of the season I switched him to Pro Plan, and then 3 months later he was switched to Purina One at his trainer.
He's never been on antibiotics.
I posted this on a facebook group and got some insight as well and I'm going to try a few different things. One of his problems may very well be that when he eats, he doesn't chew; he literally inhales it. So I'm going to try flipping his bowl over to help him slow down and maybe start chewing again. I'm also going to give a couple scoops of pumpkin. I'm also going from 3 cups/feeding to 2 cups. If that doesn't work then I'll try giving probiotics, then ultimately a change in food to something with a more appropriate protein percentage. If all else fails then I'll consult my vet again. Luckily my vet is a lab enthusiast that breeds and hunts them so I'm sure he will be able to help out
You might consider trying the probiotics now rather that waiting on other things. It can only be beneficial. Just because you have never given antibiotics does not mean it can't be the problem. Your pup was born with a sterile GI tract, so it could still be a reason since he has had a problem all his life. Yogurt is good, but considering how inexpensive probiotic supplements off the shelf at the pet store can be, the larger quantity of bacteria in a supplement, and to to give bacteria that is host specific for a dog, I personally would go with that. It sure can't hurt anything.