One of my puppies is sick

He is acting different, I recently started substituting with baby cereal and goat's milk and water because Tinkerbell is not feeding them as much, and today as I was making breakfast one of the puppies kept on crying, at first I thought it was because he couldn't find Tinkerbell but when I put him next to her, he just laid there very unresponsible and he kind of got on his back with his tongue sticking half way out and shaking (seizure??

) I picked him up and he was very limp and his tummy feels very hard, so I call the vet but before taking him in, I tried to stimulate him so he could go poo, and also gave him some puppy nutri-cal, OMG

I am so sad, I took him in to see the vet and they tried the same but he still didn't poo, they prescirbed some LACTULOSE

to make him go poo. He said he feels very constipated, they also did a stool check. What should I do?? He whines once in a while like he is in pain

I hope he gets better, he said to let him nurse from momma and just give him some formula watered down if mommy is not feeding them so much

Please someone help
