Remember that scratching is simply a symptom - and there are a whole lot of possible causes. In many cases, a single cause may not result in scratching, but put a few together a few e.g. the odd flea, dust mites, humidity etc and the scratching starts.
In dogs, the skin is the target organ for allergies - in other words when a dog is allergic to something, very often the symptom you see is scratching.
So your list of most obvious possible causes will include mites (especially sarcops), flea, contact, inhaled and food allergies to name but a few.Remember to, in the case of fleas, if the dog is allergic to fleas, it doesn't have to be covered in fleas - one or two bites will do the trick.
As your dog is so young, I would advise that you get a vet to do a work up on him/her. If this is an allergy, then the sooner you know about it the better. You also have to sort out whether the ear condition is related to the general itchiness or a separate problem.