You've had him .. 4 months or so? And have switched him 3-4 times. That's a lot. You may not be giving his body time to get used to the new food before starting him all over on another transition. However, I know that when I had my pup on a lower end food (Chicken Soup) he always had soft stools. I've since switched him to a different food and he's doing well (Blue Buffalo LBP). It may be that 2-3 cups at a time is too much food for him to digest. Maybe add another feeding in there so that each one is smaller to see if that helps? I'm still feeding my pup 3 times a day at 6 months old. You might also wait a bit longer after exercise to feed him.
Xan Varik von Fernheim (born 4/3/13)