I assume you've spoken to your doctor about this? Was the zyprexa actually prescribed prn for mania? I used to take it daily(at night), but in my case I didn't take it for mania (long story, posted elewhere...yadda yadda).......because it doessn't sound like it is working well with your rapid cycling. Is the rapid cycling part new? What I mean is, when your were first diagnosed bipolar, did you have a prolonged period of mania, or did you present right away with rapid cycling?
Are you being treated by your internest or by a psyhciatrist? I hope the latter.....that's my big thing, see a specialist!
Anyway, as for lithium, I was also on that at one time.....I know people who are bipolar and it worked wonders. I was put on it to "augment" my antidepressant, and it did not work as well. Plus, it make me "feel weird", in a way I can't really explain.. also, there's frequent blood tests, and you have to watch what you eat, sodium-wise, since lithium is a salt.
bottom line......if you haven't recently talked to your doctor about yourc concerns, give him/her a jingle. If treated properly, you can certainly work, no sweat. Ever seen that list of famous bipolars???