I had the same problem when I was preparing for the HSC just recently, and I'm afraid there's no hard and fast answer, it's different for everybody... the way I motivated myself was to look at brochures and websites for Uni degrees I wanted to get into, which would encourage me to try my hardest to study so I could go to University. The fact that you're already in University makes things more complicated, haha... do you have a dream career that you want to start after Uni, or some sort of academic award that you could strive for, or something like that? I guess you could do the same thing with those.

Sorry if this is useless :o. Hope I helped a little.