Saintly Girl, no matter what breed, most dogs grow like that. The bigger the breed the more obvious it is when they fluctuate. You'll run into the odd individual that grows in a real imressing way and have a beautiful topline throughout its growing, but the most common is that they, grow a little and look tall in the rear end, then you say ahhhhhh now he has a good topline, then four weeks later the butt is up there again. You will most likely go through that until the most intense growing period is over and they slow down. Having had large and giant dogs for years and years, and had several dogs that grow like that, I would not worry, the very majorety or the dogs end up with a good topline even if they looked like a ski sloop when growing.
Give the growing baby a big hug
Marit