If he has a wound in there it may have abscessed and this is why the vet has prescribed an antibiotic, but they don`t always work. If your concerned that Max isn`t right, I would advise calling the vet and telling them so and maybe get to the next stage of flushing/draining or whatever the vet feels is the better action to take.
If the vet knows there is fluid/puss in there and it hasn`t reacted to the Baytril, they can flush it. Max will feel better for it even though it may mean more invasive action, but what else can you do? The vet will probably know you will want Max seen again after a week anyway.
Diet-wise, always be sure there are no whole oats or anything else that might pierce or jag the pouches. I feel your worry and try not to stress too much (hugs). x Keep us updated?
