Staying motivated is difficult for many students. The best thing you can do is vary your routine :)
1. You can change your routine by changing when, where, and how you study. You could split your study time into smaller chunks throughout the day, or find time to study during your commute or while you exercise. Maybe go for a walk while you study your flashcards or find a charming coffee shop where you can do practice problems :)
2. Try working with some new materials. There are plenty of great materials out there. Take a look at this blog post for some suggestions.
3. Find a study buddy or a tutor. Having someone who is relying on you can keep you motivated. It can also be a lot more fun to study with other people once in a while.
4. Take a break. If you still have some a lot of time to study, taking a break for a few days can help you recharge and then jump back into your study plan :)
5. Set small goals for yourself. Think, "Ok, today I'm going to learn 15 new words and do 10 math problems." Breaking down your studies into smaller goals makes it more manageable and less intimidating.
Hope that helps!