Strattera is worth a try if you have the opportunity, it does work well for some individuals and has a much less propensity to get abused and as a result have tolerance development issues. (Of course the forum that deals with abusable drugs will tell you it's crap, so is penicillin if you're looking for a euphoric drug though
) It will not hurt at all to try it if you have time - at least you can say you don't like it if it comes to that.
(If you try the non-scheduled drugs first it also make it look like you're concerned with treatment first, rather than getting fun drugs, which is a good impression to leave with your doctor )
Amphetamine and its friends (dexamphetamine, methylphenidate, lisdexamphetamine) can be used on an as-needed basis, probably limited to one dose a day, and in fact is probably best used that way rather than every day on a fixed schedule. It may be more useful for you to have instant released amphetamine rather than time-released, if you're using this in an adhoc situation, because amphetamine has a long half-life on its own and you can have a disrupted sleep cycle if you're not careful to time your dosing early in the morning.
If you're using them as an aid for concentration and not as a recreational euphoriant, keeping your dose as small as feasible, and assuming you treat your body right (sleep and diet), you should be able to sustain at least a few months if not several years of amphetamine dosing with only minimal tolerance development.
I would personally avoid buying isolated amino acids unless you have a serious dietary deficiency of protein or some inborn error of metabolism, most tyrosine or 5HTP administered orally is destroyed in the periphery, outside the BBB, and as such doesn't make it into the brain. Spending the extra money on dietary protein sources is a better idea, and you'll also get other nutrients at the same time.