Long term performance is a result of many skills / memes working together. I suspect you may have noticed that the children of white collar workers are more prepared for white collar work. It would make sense that they have inherited a set of memes that help with white collar work.
Academic performance isn’t the only thing, consider your fail conditions. There’s lots of things out there to be good at.
If you’d still like to keep going, I would say just keep practicing, I reckon it’s taken me about four years to get good at my job. Look at what works and what doesn’t for you.
I found that tracking my time helped with focusing on one thing at a time, having a prioritized to do list helped me focus on the right thing, having a study group helped make learning fun, easy and consistent. Trying to fit all the knowledge I needed for a class on a single a4 sheet helped me memorize what I needed (something about the refining process).
Otherwise get good sleep, lay off the substances, get some exercise in the sun and time with friends and family and you will be right as rain.
Oh and do at least three past exams for each class. Best to practice in the conditions you will be performing in.