Need a little advise with growing pains?

I have Bull mastiff puppy he is now 10 month old and 125.4 ibs heavy ..he started yesterday to limp on his right back leg.. he scared the hell out of... the first thing this morning i went to the the vet..she told me he got growing pains..he got a shot and some pain pills for home... what else can i do to help my baby...how long do he have to take these pills...