Veterinary questions? Ask a Vet for Answers ASAP
A sudden onset of neurological signs like you're describing in such a young dog is a rare occurence and is something we need to take very seriously.
Lethargy and wobbling are not specific signs and could have several causes including an infection in the central nervous system, very high fever, neck pain, compressed spinal cord etc.
He needs to see a vet right away. This isn't something we should take a 'wait and see' approach with, or try to treat from home.
The vet will examine him and check his reflexes and mobility. They may also run some tests such as a blood test and imaging.
Treatment will depend on what is going on and may include e.g antibiotics, fluids and anti inflammatories.
If you need the details for your nearest emergency clinic please send me your postcode.
I hope this helps and please let me know if you have any further questions.