nutrition - any good books out there to recommend?

I'm relatively a newbie but I'm loving this triathlon business!  I have recently embarked on the Beginner Half Ironman training plan (now onto week 15 so five weeks in).

The workouts are certainly achievable but I am finding that some days I just have no energy or am feeling very nauseous going into a cardio workout such as a trainer session or spin class.

I know a fair bit about eating sensibly but specifics around nutrition for this sport, I'm pretty clueless.  Does anyone have any good recommendations for a book/guide to nutrition for triathletes?

Cheers!