Take a week off and see where you're at. Many athletes don't realize that they are overtrained until they regress big time. I've found myself in that hole a few times this year, and its a situation better left unexperienced.
To perform, you need carbohydrates. IMO however, CHO are highly overdone. The low/moderate CHO diet combined with a higher fat intake has proven itself time and time again to bring better performance. I've been following this diet for several months now, and I don't plan on ever returning to the wheat pasta gorge-a-thons I was previously dedicated to. Just something to consider, if you're willing to tinker with your diet.
CHO intake signals insulin release, and eventually hyperinsulinemia. Overdoing CHO will bring the lethargy you have been experiencing, and I'd suggest cutting back and introducing more fats to see how you feel.