Oh no...what a nightmare. We haven't had to deal with lice personally but have known folks that have had recurring problems and I just shudder to think of it.
I wouldn't treat myself if there were not nits, you're not supposed to do that. There are a lot of folks that think tea tree oil for example, repels lice. Claiming that they use it and never get lice. Well what about folks that don't use it and never get lice? LOL But if you're worried about it, it's worth a try, it won't hurt you.
What did the school nurse suggest? Have you tried contacting your ped? Since you already have tried the lice shampoo several times, maybe they'll have some suggestions for you? I feel like I've read you're only supposed to use those treatment shampoos once due to the pesticides in them but maybe I'm wrong. There are so many 'home remedies' that are out there - who knows if they work or not, but maybe they're worth a shot.
I agree about washing everything constantly in hot water, bundling up non-washable items in sealed black garbage bags or running them in the dryer for a bit...vacuum, vacuum, vacuum!
Our school nurse sends out packets each year with a ton of info from this site:
http://www.headlice.org/