Hello Dee and welcome to the board.
Sorry to hear you're worried about your puppy,so soon after getting him.
When you say air scratching,can you describe what you're seeing?
Perhaps your vet has mentioned SM as a possibility for his scratching,rather than any kind of formal diagnosis.
It usually takes an extensive neurological examination by a neurologist to correctly diagnose the condition.
While it is possibly for very young puppies to be affected,and we do have some members here who have had this experience,such early onset SM in babies is still thankfully rare.I would use this time between now and next Wednesday to find out as much as you can about SM in cavaliers,so you can be well informed when speaking to your vet.
Young puppies cannot regulate oil production and can sometimes have dry flaky skin.You tend to notice it a bit more in tricolours in the black hair.
A good quality puppy shampoo with something like aloe vera or teatree oil is nice and soothing for them.
If you suspect your puppy has a flea,your vet can give you a "spot on" product like stronghold which will deal with fleas and mites.
It's also possible for a puppy to have ear mites which burrow into the ear canal and can be very irritating for a puppy.Have a look into the ear and see if there's brown deposits in or around the ear. It's probably a good idea to treat cat and puppy together.Perhaps let him get over his vaccinations first.
For the moment,try not to worry.
Here are some links to basic information on cavalier health.
http://www.companioncavalierclub.co.uk/
www.cavaliermatters.org
Sins