Thank you for asking this question. It reminds me to think about my own parenting. You are entering adulthood and obviously show a desire to explore perspectives beyond your own. This is a good sign for yourself. Keep it up that way!
In your situation, there is a younger brother. I'd like to offer some ideas for you to consider:
1. Behaviors & Habits
Behaviors are based on motives & intents albeit conscious or not. They are also formed and often conforms to cultural norms and cultural biases. Go to a traditional Chinese restaurant and you will notice how the waiters/waitresses would pour tea or water for males before females although this has nothing to do with who would pay them more tips.
What I'd like to say here is at times, your parents may treat you in ways that they may not consciously realize to be unhelpful for you.
It would be natural for them to be more protective of a younger child among two children at first. In time, the protectiveness forms into habits they keep. Clothe,feed and care for this younger child may have become their automatic norm, and informs how they go about their daily lives for so long, they could not see it has affected your feelings. This may not mean they (may) love you any less. It may just mean they have become habitual in their ways of treating your younger in contrast to you.
Cultural norms as drawn from the restaurant example is also a force in itself. In many patriarchal or previously more patriarchal societies, men learned to ignore women as a matter of culture and a display of their own prestige. This doesn't mean your parents are so, but it might still inform their sense of a normal interaction, just like the order that the tea is poured.
2. The Parents Perspectives
As a parent, I have to self-remind often on being more conscious about my treatment of the siblings. I do not love any one child any less, but certainly a lot differently in how. Parenting is a lifelong endeavor. As with any endeavor, one of the key elements to success is the ability to re-assess, objectively check, make corrections, and re-chart the course. Such is life, never a straight line but we surely hold the ability to navigate its winding paths. Perhaps you can find a way to help your parents become more aware of how what they are doing is affecting you. Perhaps research some good writings on the subject and introduce them to your parents; so that it doesn't come from you and they can read it more objectively. We humans have been on earth for so long, this is certainly not a new topic. I'm sure you can find a few helpful ones. Here's a simple and easy one you can read:
How to Deal with Parents Treating Other Siblings Better
You noted an element of time, more pronounced in the past 3 years than previous, and also that your time pressure of exams, etc are weighing down on your situation even more.
There are ways to make sense of the reasons things are more pronounced that I may not understand enough to explain, but you can. For example, crucial dependency, independence differences in age, growing up, parents' perception of who can self-care and who not-yet-able and so on. These reasons may not mean they are correct nor justifiable, just possible explanations.
Too often things may fail from a misaligned sense of urgency. Be sure you hold a strong and correct sense of time for yourself, with perspective on how your life and relationship to your family will be, in 2 years, in 10 years.
I would suggest you take a look at your life-long perspective, and at the moment present, or both, to help you get through. You will move on and one day become a parent yourself. The picture will be totally different but this question might still be in you. How will you have answered it back from that day in the future? How would you want to answer it, starting now?
Wish you strength, success, and happiness in building the answers.