Hi Chelle,
*So* pleased that you found one of the good guys for your treatment!! :) Sounds like he was pretty thorough in his attention to different aspects of what might be causing you problems. -- Yes, it does seem like a good idea to get the thyroid thing checked out more -- requiring the same dose for that long is possible, but it does sound slightly unlikely (isn't it great how docs just let things go on and don't want to upset the -- maybe not helpful -- status quo?!).
Geodon is used to treat acute mania and sounds like a good option for oyu at this point in time as you're coming to treatment in a state of heightened mania and need something to act fast. Geodon has a pretty good website (http://www.geodon.com/b_home.asp) where you can check out details -- get an idea of how long you should be on it, and what possible side effects you might experience (bad side effects seem very rare with this med 
). This is more a "crisis management" med than a long-term maintenance med.
Lamictal, by contrast, is a long-term med (a mood stabiliser) that helps you maintain your balance and not slip into the crises to begin with. Again, they have a good website (http://www.lamictal.com/) with plenty of detailed info on the med itself and bipolar in general. there is only on side effect that you really need to worry about with this med, and that is a serious skin condition that can occur. However, before you panic, this is very rare: often people get a mild rash (and because it's better to be safe than sorry, they always advise that you get this checked by your doc immediately if it does appear), but mostly this is just that, a *mild* rash.
Both of these meds are well-known and have a good reputation for treating bipolar (though, as always, there are cases of people who have had problems with them). I think you may be on to a winner with this NP. (Am I imagining it or are NPs becoming more common? I always thought you had to have meds prescribed by a pdoc, but these NPs seem to be doing the same job... . Anyone know more about this?)
You might be able to get samples of meds from your NP or from the manufacturers themselves. Worth a shot -- even if it's only for one prescription (still a fair whack of money that would save you!). I think there are also programmes that you US and Canada folks can join that help with meds costs or provide free meds (based on circumstances, I imagine). If I remember one of the names I'll get back to you -- or someone else here might know. (I'm in the UK, where we have a completely different system, so I forget many of these details!).
Really happy things went so well!! 
Rosie x