Dr. Mathis has provided some great detail to your cat's problem, but I wanted to just check on something as well.
Do you have any other pets in the household? As Dr. Mathis said, fleas are good at hiding on our pets and some animals who are allergic to fleas are VERY GOOD at catching the fleas, so you end up not seeing any on that particular animal. BUT...if you take a flea comb to another pet in the household...you might find the little parasites.
Just a thought...
There are many causes for scratching at an ear. With such a young cat and always being one ear chronically, you should have your veterinarian look into your cat's ear canal. Often times a previous injury may have narrowed or scarred the canal and it becomes a recurrent problem. Excess wax may accumulate and be a physical problem of the canal or due to an allergy (often inhalant/pollen/environmental allergy). Cats that have sensitivities are extra sensitive to fleas. Using a flea collar is not recommended, as you are not treating anything more than the neck and should spend that money on something that works, specifically a product such as Revolution from your veterinarian. OTC products are often toxic to cats and I would worry about such a problem with your guy being sensitive to similar type products in a collar. These old insecticides are not very effective despite label claims.
Many cats feel itchy for other reasons and fleas and other parasites are often good at hiding on cats. Your cat may choose to scratch mainly at the ear, but be sure to have your cat examined all over other than just the ear to try to find a solution so you can avoid the e-collar use. Unfortunately without examining him, I am unable to give you an idea of which culprits are more or less likely. I hope this helps!