Here are my tips:
1. Start studying NOW, before its too late, because for any exam, 35 days is more than enough. Do not wait until the week before to begin organizing your thoughts. Depending on how well you retain information, or how organized you are, you may need more or less time.
2. Organize your binder for each subject into sections based on themes. For example, instead of having "Unit One", "Unit Two", etc., try having "Religions", "Government Systems", "Social Changes", etc., as these will be the main themes the exam will have you answering. *Remember: the point of exams is not to test you on every unit, but to synthesize information into one big overview*
3. I'm not sure how your school schedules them, but we are not assigned any homework the last two weeks leading up to finals. If this is the case for you, I suggest planning out your time hourly as to which subject you'll study when. For example, "10 am- 11am is Chemistry, 11am-12 pm is History" and so on.
4. When you are studying for multiple hours over many days, it can be hard to concentrate. Take a 15-20 min break every hour. By "break" I do not mean watching t.v. or checking Facebook, but going outside for a run or calling up a friend. In other words, do something active.
5. The night before the exam, do not stay up late studying. Remember that you have been studying for a long period of time, and now is the time to have a break before taking the actual exam. Get a good night's sleep, and eat a nutritious dinner and breakfast.
6. Finally, if you have a Facebook, Twitter, or anything of the sort- deactivate it. Better yet, cut off your internet access if possible. These social networking sites will be the death to you if you are checking for notifications every 5 minutes.
7. AND FINALLY, COMING BACK TO "LOSING INTEREST IN STUDIES"..Remember if you toil hard now, you will reap great rewards in future, just imagine the pleasure you would get when your parents see your grade in exams, and are overwhelmed...that beats all the feelings in the earth..COMMON ON GET UP AND STUDY..YOU CAN DO IT...