My 13 wk old pup, Pluto, has been eating dry Royal Canin for weeks now with no problems. I have noticed the last couple of days, he has really strained when pooping. He is still able to go, but it is very hard for him and he even yelped yesterday when we finally went.

I have read that giving a little bit of pumpkin is helpful, but I wondered if this is a common problem with this food. His bag of food is almost gone so if I needed to switch him, I figured it would be a good time to do so. I am happy with the food and he seems to like it, but don't want to fight the constipation all the time.
As far as the pumpkin goes, how much should I give him? He weighed 2.7 lbs at the vet last week when he had his shots.
Thanks for the advice!!!
Amy