It is serious. My pup had same problem, he was 2 n half months old then. I can understand your situation since its difficult to find a vet at night. I took him to vet the next morning, and he was kept on saline for a week without food. I am not sure what would be the best thing to do right now other than finding a vet for him. Other than that don't feed him anything including water let him empty his stomach that's what my vet told me. I hope he gets well soon.