you should keep supplimenting (since its a larger litter) often times moms cant produce enough to keep them all happy...I would suppliment the larger thriving pups more often and leave the little man latched as often as you can...also I would use Benebac (giving tiny amount once a day) and Nutridrops (one drop twice a day)
Benebac
http://www.revivalanimal.com/store/S...hTerms=benebac
nutridrops
http://www.revivalanimal.com/store/S...hTerms=benebac
hope your little man does better