One thing that I've realized over years is that discipline beats motivation. Motivation to work on something hardly lasts a couple of weeks, but if you are disciplined enough to wake up every morning and work on it, you'll work on it longer.

Now coming to the main question - You need to have something to work for. I did the mistake of wanting to work more without having a solid goal. Unless you have a pressing deadline or a challenging goal, human mind always tends to slack off. Think by asking yourself this question - "What is the problem you want to solve?" and then work backward and allocate time to things.