I would take all the girls out for a bit (in a warm confined place) and let the little man have the teats all by himself for about 15 min...see if that will help....its always best to suppliment the largest ones in the litter and let the little ones have the teats... if you have nurtidrops put a drop on your finger and wipe it into his mouth...if not use karo and give him the smogasbord
hope this helps