Please make sure that you're not feeding too much as that can cause diarrhoea as well (remember that the feeding amounts on the dog food packets are guideline amounts only & every dog is different), a little and often (5X per day) is better than 2 big meals. I think as well that a natural diet (eg RAW or BARF) is the best for your dog, but it's not always possible (I drive a truck so it's not practical for me when I'm away working), also it can be more difficult to feed the right amount when feeding a natural diet (especially with regards to overfeeding calcium & phosphorus). I have fed Orijen to my 7.5 month old pup since I've had her & she is very healthy, I'm very happy with it although it is expensive.
Do a lot of research on the internet as well, I would never just listen to any vet's advice about which food to give as they are nearly always sponsored by one or other of the pet food makers. Everybody has a different opinion about dog foods & of course everybody thinks that they are correct
. If you do choose to feed dry food then of course make sure it is for "Large Breed Puppies" as this is especially important with regards to not overfeeding calcium & phosphorus.