If you are exhausted, that may be a sign that you are OVERTRAINING. Contrary to popular belief, more is not better with exercise. If you have to push through it, then you are overdoing it.
Check out this article that explains the signs of overtraining, and when to back off: www.sparkpeople.com/resource/fitness_artic
From the article:
"The cause of overtraining is simple. You’re not resting enough to allow your body time to recover, or you’re doing the same exercises too much. Here are some common symptoms of overtraining:
Feeling tired, drained, and lacking energy
General body aches or mild muscle soreness
A decrease in performance
Inability to complete workouts
Lack of motivation"
Your body and mind get stronger through rest... not exercise! Working out more will not make you lose weight faster, either.