Are you getting enough minerals? Training can really take 'em out of you. Try adding a multi-mineral supplement to your vitamin regimen. I noticed a big difference when I started this. I use Twinlab multi-mineral.
Something else, I wouldn't train "heavy" every week. I alternate between heavy weeks and not-so-heavy weeks. Also, I change my whole routine every 2-3 months, and I probably take a whole week off from lifting about every 4 months due to going on vacation, where I may do other active things but not weights.
It's when you're resting that your body repairs itself to come back stronger. Everyone's different in regard to how much rest they need.