That makes a lot of sense. Olanzapine (Zyprexa) is a strong antagonist at the H1 histamine receptor (which tends to cause significant sedation) and an inverse agonist at 5HT-2A (which may contribute to sedation, but I'm not sure). I'm glad that it works for you, but I'd be fairly nervous about using olanzapine long-term to manage insomnia and stimulant use. Antipsychotics are very dirty drugs, and they tend to do a whole bunch of things at a whole bunch of receptors. They gain a significant chunk of their therapeutic action from D2 (dopamine) antagonism, but blocking D2 can also cause a wide variety of fairly nasty side effects in people, including akithasia (similar to restless legs syndrome, but more generalized and worse) and tardive dyskinesia (permanent involuntary repetitive movements) are a serious risk with long-term use. Olanzapine specifically also does a bunch of things to muscarinic receptors that can cause massive weight gain and diabetes; the amphetamines will probably offset the weight gain but won't protect you from the risk of diabetes.
In general, if you really need to sleep there are better things out there to use. Benzos and z-drugs (zolpidem/zopiclone/zaleplon, sold as Ambien, Lunesta, and Sonata, respectively) are an option, and they're nowhere near as dirty as antipsychotics are. There are risks associated with memory impairment, blackouts, and associated stupidity if you go overboard with them, and there are also risks of dependency and/or addiction if you use them too much or for too long (also withdrawals from GABA agonists such as benzos and z-drugs can be really ugly if you're seriously addicted). You could try getting a script for suvorexant (which operates through orexin receptors rather than GABA; it basically switches off a receptor in your brain that keeps you awake rather than banging on things that put you to sleep); that one's fairly new, schedule IV, and not super well studied but worth a try if you'd rather not bang on GABA. Finally, melatonin is completely harmless (although it may not be super effective); it's a hormone your body produces when it's ready to go to sleep and it's basically impossible to OD on. If I were you I'd start with melatonin and then carefully try suvorexant and/or benzos.
