Just a couple points that ought to be made here -
First, you are self-medicating which is never a good course of action because, among other things, you really don't know how much, if any, adderall you should take to counteract the negative tendencies you have (e.g. inability to stay focused) without impairing your strongest attributes. To say that a doctor would probably diagnose you based on the list of "symptoms" posted by dmitrik4 is meaningless. Adderall is one of the most highly regulated prescription drugs on the market because it is so casually abused by people with the exact same mind set as the one you profess. If you need it, a doctor will give it to you. To rationalize your failure to go an get a diagnosis and obtain a prescription by saying that you don't want to be bound to taking it borders on idiocy for several reasons - first, a prescription does not mandate use, far from it. In reality, it gives you the power to choose when you take it. Second, taking adderall without a prescription is illegal, and possession of a controlled substance without a prescription is illegal. Being that you hope to pass the moral fitness review to be able to sit for a bar exam, it would in your best interest to cross the t's and dot the i's on this issue, cause one stroke of bad luck could put you in a very bad position. Third, as i stated above, you don't know what is a good amount for you and what is a bad amount for you, assuming that you do in fact need it. A doctor can shed some light on this for you and find the ideal dosage for you, and contrary to what you might think, if you express to your doctor that your intention is to take it primarily when you have finals or serious work to get done, not only will that not preclude your obtaining a prescription, but they can probably give you some really good insight on how to get the most out of it.
Secondly, there seems to be a large contingent of people on here with the "holier than thou" mindset, who think that taking adderall borders on blowing a line of coke. To those people i would simply say that you should be thankful for your abilities, and thankful that its not something you need. I would also point out that some people do need it, that while over diagnosed, ADD is a real condition, not just a cop out. I would recommend reading up on it and educating yourself a bit more before throwing out sweeping generalizations. To claim that adderall is the same as coke is like claiming that taking advil for a headache is as bad as smoking opium, they aren't anywhere close to each other, save only that they are both stimulants.
Third - all this talk of habit forming and tolerance - speaking from the standpoint of someone who has taken adderall consistently for close to a decade I can attest to it being habit forming to the extent that when you stop taking it suddenly you will feel very lethargic and tired for several days, but it is not addictive in the sense that you go through painful withdrawals and cravings or anything of that nature. On the other hand, I can also attest to the fact that if you take it AS PRESCRIBED you do not build up a tolerance to it. I have taken it for ten years, and i take the same dosage now as i did ten years ago, and it is just as effective.
In summary, while i understand trying to give yourself an edge, there are other, safer means of doing so than self-medicating with black-market pharmaceuticals. You obviously will do what you want, but personally, i would really recommend going about it the right way rather than the wrong way.