Having backlogs is very exhausting.

To cover backlogs, increase your study hours and attend one shot lectures available online for free. After attending a one shot lecture most of your topics will be cleared. If you have a few doubts you can watch a detailed explanation on that specific topic. After you're done attending lectures, practice questions of that chapter. Focus on quality over quantity during this time. Solve questions based on the pattern of the exam. Focus on solving questions asked in the previous years of that exam. While completing the already existing backlog, try not to create more by avoiding the current syllabus. 4 months is quite enough time to cover you backlogs. You can easily do that.