Growing pains in young large breed puppies are common, and there are a few things you can do to help.
We have had a couple of puppies from last fall litter that started limping recently and some families were really worried about their puppy, one vet even suggested to a family there puppy had double elbow dysplasia, (without even an xray ) and they were devastated. After xrays it was later determined it was Pano, or growing pains.
While hip and elbow dysplasia can be genetic, environment plays an even bigger part in a young growing puppy. Health testing of breeding pairs greatly lessen the chance of hereditary genetics passing this on, but nutrition and gentle exercise are the main players in the healthy development of your puppy. We have found, though some may disagree, putting your large breed puppy on complete balanced raw food or large breed adult kibble works best to help slow down the huge growth spurts they go through from 4 to 7 m0nths,
Putting them back on puppy kibble when the massive growth spurt has slowed down. Limited exercise during this time is also critical, especially when lameness occurs, 24 hours of rest is needed and possibly a vet visit to ensure no damage and get some inflammation/pain meds such as Metacam. Duck and turkey necks and feet are a good source of collegen and glucosamine for your puppy, we feed them frozen and they love them. meaty knuckle bones are good too and keep them occupied when they need their down time. Check out the links below for more information about Pano. The BMD info is a great post.
http://www.bmdinfo.org/Health/Limping-Panosteitis_and_HOD-Bernese_Mountain_Dog.php
https://vcacanada.com/know-your-pet/panosteitis-in-dogs