Based on your description of the problem and your kitten’s background, your kitten most likely is suffering from ear mites. Ear mites are parasites that cause itching, scabbing, and wax around the ears. They are common in kittens–especially kittens that come from less-than-perfect backgrounds.
Before I go further, I should say that if you can possibly manage it your kitten will definitely benefit from a veterinary checkup. The vet will be able to assess the ears, as well as perform a general health evaluation. Kittens that are born in barns frequently are infested with intestinal worms that may be contagious to human beings. And kittens needs shots to prevent deadly diseases such as feline panleukopenia virus (also known as feline distemper). So, plan A is to see a vet. No doubt about it. The vet can prescribe a medicine such as Revolution or Advantage Multi that will eliminate ear mites as well as intestinal worms. And she or he can vaccinate your kitten.
If going to a vet is absolutely out of the question there are other, albeit inferior, options.
Some pet stores sell over-the-counter ear mite medicines. These medicines are not as safe or effective as the ones that vets can prescribe, but they might help with the ear problem. Most of these medicines need to be applied daily for at least a month.
As well, over-the-counter dewormers are offered at some pet stores. Like the ear mite medicines, they often are not as safe or effective as the ones that your vet can provide. They also are not as effective at preventing spread of the parasites to humans.
And then there is the issue of shots. In many states, you can buy vaccines at pet or feed stores and administer them yourself. Kittens should receive at least two (preferably three) vaccines against panleukopenia at three or four week intervals.
If you work hard and are resourceful, you may be able to tackle your kitten’s problems on your own. But in the long run, it may be less expensive (and certainly more convenient) to go to the vet. And there is no doubt whatsoever that a veterinary checkup would be in your kitten’s best interest. If it is at all possible, then please do it.