concerns about my puppy- Plz Help

My puppy is 5 months old and has just started pooping immediatly after he eats. I mean he eats and walks to the door, I take him out and he poops. WE havent changed his food or anything else in his diet. He doesnt act sick but it worries me b/c he just started doing this a couple days ago. Prior to this it would take him a couple hours to poop, but now its almost immediate.
   
Any advice is greatly appreciated.

what kind of food are you feeding him? he might have jst have something wrong with his digestive system.
   
Is his poop solid or runny? if its runny he probably needs a different kind of food.
   
if things get worse i would take him to the vet.