When you first begin prepping for the GMAT, staying motivated is easy. But after a couple of months, it can be difficult to keep yourself motivated as you continue to try to improve your score.
If this happens to you, there are a few strategies you can use to regain your motivation. First, you can remind yourself why you are doing all this work. It is easy to get into a rut in which it seems you are simply taking the GMAT for the sake of the GMAT. Remind yourself of your ultimate goal: to get into business school. Tell yourself not only that you need to study for the GMAT to get a high score, but also that it is that high score that eventually will lead to your admittance to the business school of your choice, which in turn directly affects your employment prospects after graduation.
If this mental boost is not enough, it is possible you are being discouraged by the difficulty you are having with the problem you are trying. Remember, you are doing those problems precisely because they are difficult for you. In order to get your confidence back up, do some work on reinforcing your strengths. This will have the added benefit of ensuring that you do not miss questions in areas you did not study as much because you were stronger on them to begin with.
If neither of these methods helps, a final motivational strategy is to create intermediary goals, rather than just thinking of the score you want to achieve. For example, you could create a goal of understanding the basics of probability by the end of the day and work towards that. When you accomplish these smaller goals it will boost your confidence and keep you motivated.
By using these techniques you should be able to keep your motivation up all the way until test day and get the most out of your studies.