dextrose/maltodextrin are forms of carbs. You need carbs before and after workouts. Carbs before hand give you energy to fuel your workouts. Carbs after work to spike your insulin which drive protein, aminos, etc... into your muscles. Most suggest around 20-40g before the workout and 50-100g after.

And you say you feel exhasuted towards the end of your workouts. Are you taking in carbs before the workout? If not, start there. If you still feel fatigued, sip on some carbs such as a gatorade throughout the workout.

Have you read the stickies? Read those as this is covered in them, namely the "How to Bulk" and "Pre/Post Workout Nutrition" ones.