In terms of writing essays, you should probably adopt a more pragmatic approach which I believe is evident considering the difficulties you are facing in interpreting the questions as well as not being able to write an essay in 45 minutes.
I don't think there's an ideal way to study for English, since each student may be comfortable with different study methods and may adopt different study strategies as a result. However, I do think that making the appropriate changes to your study methods will allow you to progress and study more effectively.
Preparing and memorising a thorough analysis of your texts where applicable may be a more effective and efficient way of preparing and writing your essays in a timely manner. Knowing your analysis implies simultaneous knowledge of both techniques and quotes. In addition, you won't need to worry about having to construct complex sentences while you're doing your exam, which will allow you to save time you would otherwise spend on thinking about how to express your point in a written form. Knowledge of your analysis prior to your exam will also allow you to complete your exam using a much more flexible approach, as you'll be able to adjust your analysis (including introduction, conclusion and links to the question) depending on the question.
Memorising depends on how you're used to retaining information. When I did my HSC, I memorised my analyses by memorising one paragraph at a time, which I did by constantly reading and repeating, and then trying to say my whole analysis when I've memorised all paragraphs. Once I was confident that I 100% knew my analyses, I started to write my analyses under timed conditions and kept doing so until I was able to write them in a timely manner.
In terms of knowing themes and being able to interpret the questions, and as mentioned above, you should definitely seek assistance with those as these remain essential components of your response and having a thorough understanding of them is essential. This is manifest in the form of questions and feedback you receive from your teacher. There are of course several people on here who are very good at English who may be able to help you more directly as well.
One last thing, never feel hopeless. You still have time to improve and you can definitely improve!
I hope this helps!