I agree with the two answers here already by Carmen and Destiny. I also want to add that maybe the process you have been taking doesn't stimulate your mind. For example, if your usual process is to just start writing and see what comes out, you could try writing an outline first and see how that goes. If you've been writing an outline first, start your next essay by just dumping all your thoughts out, then see what you can do with them once they are all out on the page.
Another thing to keep in mind is that a lot of people tend to overcomplicate the process, and end up overwhelming themselves. When you think of an idea you want to put on the page, write it as simply as you can and don't even worry about style at that point. Complicated sentence structures and big words should only be used when necessary.
Importantly, editing and revising are the true MVPs of the whole process. A rough draft is almost never any good, and it usually takes at least three drafts to get a paper to the point of being something worth reading. Because of this, I want to really emphasize the point I made about just getting your ideas on the page in the simplest form possible... you'll have plenty of time to change the way things are worded later.
You can be good at writing, but it does take time to hone this craft. If you work hard to improve your writing and you just find it to be tedious and incompatible with your true strengths, that's okay. If you really hate it, it's okay to just do it well enough to get the grade you need. What's important is that you learn something from the process of improvement.
With regards to understanding literature, the issue could be that you are reading it too fast or that you are reading stories that are uninteresting to your tastes. If you simply find the books you're reading for class uninteresting, you can try to get through it by researching the authors and historical contexts of the stories. That can give you a new vantage of them, and maybe even provide insight into why they were written.
The number one question you should ask yourself when analyzing literature is: Why did the author write this story? In other words, what insight are they trying to share? A good start to answering this question is to pay attention to how it makes you feel. If it doesn't make you feel anything, try to figure out what the author wanted you to feel. Imagine they are a bard standing in front of you telling you a lengthy tale--How are they looking at you? What is their intention?
Lastly: Reading will make you better at writing, and writing will make you better at reading.
Thanks for your question. I hope this helps!