one of our 6 puppies is having a hard time latching on....
Hi
Sometimes a pup may have a problem with his palate (perhaps a cleft palate) which can cause difficulty in sucking and drinking.
I'd recommend that you have this puppy looked at by your veterinarian so that you can find out if there is such a problem. If so, tube feeding can help but it's something that your vet would need to show you how to do.
If necessary there are surgical options, but if your pup is actually nursing and so on, it may be a minor cleft, or could be something quite different. Only your vet can make an accurate diagnosis, so I'd recommend getting an appointment asap.
Best of luck, hope he grows up big and strong.