Lucky's had his bouts with it. The first time I was terrified because I had let him out on a few occassions and thought I'd exposed him to Parvo or something! He'd had 3 sets of immunizations but because of his age he was still at risk.
Lucky was even a bit less playful than usual (but later I realized it was a hot day and the A/C wasn't on .... realized that after I turned on the A/C and he perked up!!!)
I called the emergency vet here and the advice they gave me was to to watch him and give him the chicken/rice as you are doing. They also suggested I take his temperature - which I did. Walked to the pharmacy & got a super fast digital thermometer that takes an accurate temp in 9 seconds and some vasoline. The vet told me the "normal" temp for a puppy and Lucky was normal. I called the vet's office (this was 9pm or so at night), and they didn't think I needed to bring him in but see how he was the next day.
The next day he got better, and then it came back a week later and we've had bouts of it on and off ever since. He's usually been good on the rice & chicken baby food, but when we ween him off that his stools got loose again. He's had 3 fecals in the last few weeks - all negative for parasites.
Finally, the vet gave him a prescription diet. Eukanuba Low Residue Puppy. It is supposed to be for puppies with sensitive digestive tracks, and I am happy to report it is working for Lucky. I'd like to have him on a higher quality food with no animal bi-products, but for now, I'm happy that his stools are firm so apparently for Lucky it was just a food sensitivity.
I did a post on Sensitive Stomach diets, and it seems Lucky and Kingston aren't the only ones with runny poo - how bad is the diarrhea? Can you call your emergency vet in your area for advice about whether you need to bring him in?
In any case, if it does not clear up, you might want to talk to your vet - if he's otherwise healthy maybe the vet can test for parasites and if those are negative, then perhaps it is just a diet issue.
Good Luck