Stimulants are almost always a bad idea in bipolar, unless you have ADD/ADHD and can't manage it without them, and even then it's usually necessary to combine them with an antipsychotic and/or mood stabilizer.

Even large amounts of caffeine can be bad. I have been known to self-induce hypomania, or keep it going, by drinking large amounts of coffee in the evening and then not sleeping. And I'm not even particularly sensitive to the effects of caffeine.....I can normally drink caffeinated beverages throughout the day without getting jittery.

By all means, tell your doctor about feeling tired all the time; maybe s/he can tweak your current meds to make your cocktail less sedating. I understand your frustration with memory loss and being unable to focus---I have the same problems and they piss me off to no end! But as both a nurse and bipolar patient, I can't recommend going on stimulants just for that purpose in the absence of an attention-deficit disorder.....it's just asking for trouble, as it's too easy to flip into mania on the drugs. JMHO.