My GSD growing too fast it hurts him?

The vet called it p (i don't even knw how to spell it). It happens everytime my dog's bones grow too fast (on his legs) and he would be limping. I hate seeing him suffer like that. I gave him aspirin for dogs, it helps him settle down more. He would lie on the couch all day. The next day he would be limping again. So, what kind of food do you suggest I should give him and the things that I can do that would help at this time. The vet said it's nothing to worry about, but I just want to make him comfortable at this difficult stage of his growing.