Not sure ruffly what level you are at, this may seem a bit advanced, but still you might get some ideas that may help when setting about your essay. It is something I wrote for my introduction when I made a book of some of my essays.
Here are a few tips for essay writing - have a good idea of what you want to say before starting to write and stick to the point. Sometimes we are tempted to include something we feel is interesting but does not belong in the essay, so avoid putting it in. If you are asked to write about three pages or about a thousand words do not write much more than you need to, unless you feel absolutely necessary. Some students do this to impress their tutor, but they are only wasting the tutors time and their own. Most of my essays have been at least 100 words short if not more and I have still passed.
When you are setting off to go and do your essay avoid taking to many notes from the material you have studied, this is rather like an excuse to avoid doing the essay. If you have a good idea what you want to say, then you will have a fairly good idea of the notes that you need to take.
Always make a note of the title of the book, publisher and page number when note taking. If you do this, you will save a lot of time; rather than end up wasting precious time later searching to find where you got your notes from when you need to include a bibliography or reference.
Bear in mind teachers do want you to pass your course - it always looks good on them. I hope this will be of some use to you in your studies.
You might like to consider feminism, genetics, (Frankenstein) faith and beliefs, how important is the author in determining meaning, war and politics, gay movement, escapism in books or films, essay on poetry, sociological issues is a wide area for debate, myths and ledgends, something from Shakespeare, Macbeth best tragedy ever, or Dickens, his book The Mystery of Edwin Drood is probably still best mystery ever written.
But as you only have 3 weeks pick something you know lots about and would enjoy writing about it.
Hope this will be of some help; all the best with it!