Same here. I'm working on my MBA. Once I finish work its off to class until 9pm. Add a newborn baby and my life gets more interesting. Getting up early would have been an option if I didn't have the kid so I have to get as much sleep as I can in between night feeding/care etc. Some days I'm so exhausted I'd prefer to stay in bed rather than go to work but I drag myself through another day anyway. The treadmill at home helps a lot. So far I manage to get in a workout at the gym on the days I don't have class but as you said the intensity varies. Some days I have energy to spare and other days its a willpower test just to get through a decent workout.
Having done it i can attest to the fact an MBA is totally draining. I suggest that you try to get more of the workouts over the weekend and less during the week, and add some weights at home if the gym's not easily gotten to.