I'd be a bit concerned.. That is not typical puppy behavior.
It's important that larger breed (60lbs+) puppies to not be allowed to grow to rapidly, as these breeds have an inherently higher risk of early-onset skeletal problems than small or medium breeds... it is believed that slowing the growth of large breed dogs offers some protection against many of the bone diseases and defects that plague large breeds.
There are two causes for these bone related problems... Genetic predisposition and overfeeding or over-supplementation in the diet. In response to the latter concerns, manufacturers have developed special "large breed" puppy formulas designed to prevent developmental bone disease, by controlling calcium-phosphorous ratios and calorie intake...
To make a long answer short... If your pup isn't on a large breed formula, I'd consider switching him over to one... And even if he is... I'd get him checked out and possibly x-rayed to rule out any skeletal problems as the cause for his periodic malaise.
